Preheat the oven to 350 degrees F. Butter an 8-by-8-inch baking pan with the 1 tablespoon butter.
Melt the chocolate with the butter and cream in a double boiler. Once melted, remove from the heat and mix in the marshmallow creme and sugar with a hand mixer. Mix in the eggs, one at a time, and then the vanilla.
In a large bowl, sift together the flour, baking powder and salt.
Fold the dry ingredients into the wet, and pour into the prepared baking pan. Sprinkle the top with the chocolate chips.
Bake until the edges just start to pull away from the pan, 30 minutes. Let cool to room temp before slicing.