Stir in flour, zest, salt, and baking powder. In another bowl, beat the egg with sugar for 5 minutes. Add vanillin, butter, juice, and milk. Beat again. Add dry ingredients to liquid ingredients and mix.
Divide the dough into 2 parts. Add chocolate melted in the microwave to one. And to the other chocolate pieces.
I use paper forms. If not, grease the mold with butter and sprinkle it with flour. Remove excess. First, we spread a spoonful of light mass, then chocolate, again light, and again chocolate. With a wooden stick, we make circular movements in each shape. We bake for 17 minutes at 180 ° C.