Melt the chocolate and stir the in the cocoa powder. Set aside.
In a medium bowl, stir together the lebkuchen spices.
Make the muffin batter
Arrange 2 racks in the oven so that they divide the oven into thirds.
Preheat the oven to 350 F (or 325 F if baking convection).
In the bowl of a stand mixer, whisk together the flour, baking soda and baking powder.
Add in the sugar, eggs, butter, vanilla extract, and yogurt. Using the paddle attachment, on high speed, beat together all the ingredients for 2 minutes - until light and fluffy.
Scrape down the sides of the bowl as needed.
Pour 600 grams of the batter into a medium bowl.
Add the melted chocolate with cocoa powder and milk to the batter that is still in the stand mixer bowl.
Beat on high once more to combine all the ingredients. Scrape the sides of the bowl and mix again, just briefly.
Add the mixed spices into the second bowl of batter and stir together with a spatula.
Bake the Muffins
Line 2, 12 cup muffin pans with muffin liners.
Using a tablespoon scoop - scoop alternating lebkuchen and chocolate batter into each muffin cup. For 24 muffins, scoop 2 of each batter into each muffin cup.
Use a skewer or knife to gently spread the batter around each muffin cup.
Bake on the pre-placed racks for 20 minutes, or until a toothpick inserted in the center of the muffins comes out clean. After 12 minutes, rotate and switch the pans 180 degrees to ensure even browning.
Once they are finished baking, let them cool for 5 minutes before trying to flip them out of the pan.
Once cooled, optionally drizzle the muffins with melted chocolate.
Notes
These will stay fresh for 4-5 days if kept in an airtight container at room temperature.