Plum Bars with Oat Streusel

Jammy, plum bars with a poppyseed oat streusel crumb topping, these plum bars have all the flavors of the end of summer in one cute little bar. The addition of poppyseeds into the streusel on these bars is quite possibly my favorite part and is completely thanks to Ruth Tam’s Sour Cream Blackberry Bars!

What types of plums should you use for baking?

There isn’t really one right answer but for me these plum bars are best with Italian prune plums. However, they can be difficult to find and somewhat expensive especially in the US so you can substitute other plum varieties, simply note they make take longer for the moisture to cook out.

Should I use a metal or glass baking pan?

Most of the time I find that metal pans work best for baking because they distribute the heat quickly and evenly to the bake. I haven’t tested these with a glass pan but would not recommend it.

Can I leave out the poppyseeds?

The poppyseeds in the streusel of this plum bar are very optional but I HIGHLY recommend adding them in. They aren’t overpowering but you still get a little bit of the nutty after taste.

What can I use instead of sour cherries?

For one you can simply omit the sour cherries from this recipe and instead add more plum butter if you have mored cooked. Alternatively, almost any berry or even fresh plums will work in place of the cherries.

Tips for Plum Bars

• Cook the plum butter in a heavy bottomed pot to prevent it from burning – just be sure not to use an uncoated cast iron as the acid from the fruit will break it down.
• Don’t leave the plums unattended on the stove for more than 5 minutes, especially once they start to reduce because the fruit sugar and added sugars will burn easily.
• Don’t skimp on the plum butter, if you feel like you could add a bit more, do it!
• I only recommend making these in a metal pan because glass pans will cause the bars to bake unevenly and they will steam more than crisp up.
• If you want clean cuts the bars need to be FULLY cooled. If you cut them while warm they won’t be as firm.
• These are best stored in an airtight container in the fridge or at room temperature.

Additional Cake Recipes to try!

• Plum Upside Down Cake
• Red Currant Cake | Johannisbeer Streuselkuchen
• Apple Streusel Bars | Apfelstreuselkuchen

Ingredients

• Italian Prune Plums: Also known as italian plums, blue plums, or sometimes even purple plums, these are a very specific type of plum used in German baking that is only in season for a brief time. However, regular plums will work too they just need to be cooked longer.
• Granulate sugar: White sugar is used in both the plum butter as well as the bar base and streusel.
• Cinnamon: A little ground cinnamon can be added to the plum butter if you want that fall warmth but you can also leave it out.
• All Purpose Flour: Any all purpose flour should work for this recipe but my go-to is King Arthur brand.
• Whole wheat flour: This is completely optional but using part all purpose flour and part whole wheat flour adds a nice bit of flavor and texture to the bars. That being said the whole wheat flour can also be replaced with all purpose flour in this recipe.
• Salt: a little salt helps to balance out the sweetness of the bars.
• Butter: Unsalted butter, that is quite soft aka at a warm room temperature is best for this dough because it makes it easier to mix in with the dry ingredients.
• Vanilla Extract: A little vanilla enhances both the sweetness and flavor of the plum bars.
• Sour Cherries: Frozen, fresh, or jarred sour cherries will work in this recipe. They can also be substituted with other berries or simply add a bit more of the plum butter.
• Poppyseeds: Ok so these are optional but I actually love the poppy seeds in this streusel as they add a nice little nutty flavor to balance out the more tart fruit and sweet streusel.
• Oats: Rolled oats are best for the streusel and add a beautiful crunch to the bars once baked.

How to make Plum Bars

Pflaumenmus (Plum Butter)

• The night before you plan to make these bars (or up to 5 days in advance), you need to macerate the plums so they can be cooked into a plum butter the next day.
• To macerate the plums, rinse and dry them. Then remove any stems and cut in half lengthwise around the pit to remove it. Place all of the pitted plums into a large pot or bowl. I used a coated cast iron dutch oven which works perfectly but don’t use one that isn’t coated as the sugar and acid will be too much for the exposed iron.
• Pour in the granulated sugar and stir to combine. Optionally add in two teaspoons of cinnamon at this time.
• Cover the pot or bowl and leave it to sit at room temperature overnight.
• Place a small plate in your freezer, this will be used to test the plum butter.
• When you are ready to cook the plum butter the next day, remove the cover and place the pot with the macerated plums (if they were in a bowl, transfer them to a pot at this step) over the lowest heat possible.
• You want to cook this plum butter low and slow, stirring frequently to prevent the sugar from burning. This takes about an hour but could be a little less or more depending on how many plums you’re cooking.
• Continue cooking until the mixture has thickened to the point where you don’t really see any plum juices running around.
• To test the doneness of the pflaumenmus, take the plate out of the freezer and spoon 1 tablespoon of it onto the plate. Allow it to sit for 30 seconds to a minute. Then, when you wipe the jam off with your finger it should wrinkle and be quite thick.
• Once cooked, remove from the heat and pour the plum butter into an airtight container and store in the fridge until ready to use.

Bar Base

• Preheat the oven to 350 F and place a rack in the center of the oven.
• In a large bowl, whisk together the all purpose flour, whole wheat flour, granulated sugar, and salt.
• Add in the butter and vanilla and use your hands or a fork to rub the dry ingredients into the butter until fully combined and no dry bits remain.
• Line a 9″x9″ metal pan with a rectangle of parchment paper that is 9″ wide and 15″ long, sort of like a sling.
• Crumble just slightly more than half of the dough into the lined pan. Spread it out evenly across the bottom. Use your hands or the bottom of a flat measuring cup to firmly press the dough into an even layer.

Streusel

• With the remaining base dough, pour in the poppyseeds and oats.
• Use the fork or your fingers to mix it all together and create clumps.

Assemble & Bake

• Pour the plum butter over the top of the base and spread it out into an even layer.
• Sprinkle with the defrosted or drained sour cherries.
• Finally crumble the poppyseed oat streusel over the top.
• Place in the preheated oven to bake for 30 minutes. After the timer goes off, rotate the pan 180 degrees. Then bake for another 25-30 minutes until slightly golden brown on top.
• Remove the pan from the oven and allow the bars to cool completely to room temperature.
• Once cooled, run a knife along the two sides that don’t have parchment to loosen the bars if necessary.
• Use the parchment paper excess to lift the bars out and onto a cutting board. Cut the bars into 12 or 16 equal pieces.
• Store in an airtight container in the fridge for up to a week even once cut.

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