In a mixer bowl, beat the butter and sugar. We introduce eggs, then pour in melted chocolate.
Sift the flour and combine with baking soda and baking powder. We introduce half into the butter-egg mixture and knead, add kefir, mix and add the remaining half of the flour.
Make crumb from the remaining chocolate. We send it to the dough and mix.
Fill the muffin molds with the resulting mass, without reporting to the top by 2-3 centimeters.
We bake muffins in an oven preheated to 180 degrees for about half an hour.