Preheat oven to 350 degrees. Line standard muffin tins with paper liners. Whisk together the flour and baking powder and sift; set aside.

Cream the butter and brown sugar. Add the eggs gradually; stir until well mixed(emulsification). Add the yogurt and stir until smooth.

Add the flour mixture to the liquid mixture and use a rubber spatula to mix until smooth. Add the chocolate chips and peanut butter to the dough and swirl with a spatula for a marbled effect.

Divide the batter evenly among the lined cups.

Bake for 20(+6) min, rotating the tins halfway through. Transfer tins to wire racks to cool completely before removing the muffins.

More Details at
http://www.chez-k.org/english/muffins/chocochip-peanut-butter-muffins/