Preheat oven to 350F. Generously grease and flour a 10-inch ring mold. In the top of a double boiler over low heat, melt the chocolate.

Place the butter, peanut butter and sugars in a large bowl and mix with an electric mixer until light and creamy, about 3-5 minutes, scraping the sides of the bowl occasionally. Add the eggs one at a time, beating well after each addition.

In a medium bowl, stir together the flour, baking powder and salt. Add to the butter mixture alternately with the milk until just blended.

Pour half of the batter into another bowl. Stir the melted chocolate into one half of the batter until well blended. Stir the chocolate chips into the other half of the batter.

Using a large spoon, drop alternate spoonfuls of chocolate batter and peanut butter batter into the prepared pan. Using a knife, pull through the batters to create a swirled, marbled effect; do not let the knife touch the side or bottom of the pan and do not overmix. Bake the cake for 50-60 minutes, until the top springs back when lightly pressed. Cool in the pan on a wire rack for 10 minutes, then turn out onto the rack and allow to cool completely.

To prepare the glaze, combine all the ingredients in a small pan. Melt over low heat, stirring until well blended and smooth. Cool slightly. When slightly thickened, drizzle the glaze over the cake, allowing it to run down the sides.