Whisk the cheese and butter until fluffy. Continuing to beat, first add sugar in a thin stream, then beat the eggs one by one and add a spoonful of sour cream.
Melt the chocolate in a water bath or in a microwave oven. Divide the dough into 2/3 and 1/3. Just divide the flour. Add the chocolate and 2/3 of the flour to 1/3 of the dough. Add 1/3 of the flour to 2/3 of the dough. Mix separately first.