A few hours before you start, take two cups of mini marshmallows and put them in the freezer. Take out two sticks of butter and let them come to room temperature.

Preheat the oven to 325F.

In a large bowl, mix the flour, baking powder, and salt and set aside.

In a second bowl, add the butter, eggs, brown sugar (firmly packed), granulated sugar, and vanilla. Beat on high for two minutes. Break the chocolate into squares, and melt in a double broiler, or microwave on high for one minute. Add the melted chocolate to the wet ingredients, and mix until completely incorporated.

Mix the dry ingredients into the wet in thirds.

Crumble the walnuts. and fold into the dough. Chill for 30 minutes.

Take the marshmallows out of the freezer. Use about two tablespoons of dough and press three mini marshmallows into the center. Ball the dough up and around, completely covering the marshmallows.

Bake for about 8 minutes, until the cookies are just barely cooked. If you overcook, the marshmallows will melt and dissolve. The cookies will still taste great, but you won't get the nice white chewy marshmallow center.