Rinse the berries well and drain all the water.
For the dough, melt the butter and mix it with eggs, sugar and kefir, whisk a little and add soda and flour. Knead the dough and add the berries.
Put the dough in greased tins, while leaving space, as the muffins will rise during baking.
Bake muffins on kefir with berries for about 30 minutes, heating the oven to 180 degrees. Check for readiness with a toothpick. Ready muffins can not be immediately removed from the molds, wait 10-15 minutes so that they do not lose splendor.