Preheat oven to 375 degrees F.
In a large bowl, stir together the flour, brown sugar, baking powder, and salt. Cut the butter into 1/2-inch cubes and distribute them over the flour mixture. With a pastry blender or two knives used scissors fashion, cut in the butter until the mixture resembles coarse crumbs.
In a small bowl, stir together the peanut butter, milk, eggs, and vanilla. Add the peanut butter mixture to the flour mixture and knead until combined. Knead in the peanuts. Pat the dough out into a 1/2-inch thickness on a cutting board.
Using a floured 2-1/2-inch to 3-inch diameter crinkled round biscuit cutter, cut out rounds from the dough. Gather the scraps together and repeat until all the dough is used and there are 16 rounds.
Place 8 of the rounds on an ungreased baking sheet. Top each round with a piece of the chocolate and one of the remaining circles of dough. Press the edges gently to seal.
Bake for 17 to 19 minutes, or until lightly browned. Remove the baking sheet to a wire rack and cool for 5 minutes.
Using a spatula, transfer the scones to the wire rack to cool. Serve warm or cool completely and store in an airtight container. Yield: 8 scones.
VARIATION: Make the dough as above, omitting bittersweet chocolate, substituting 1/2 cup unsalted whole peanuts for the chopped peanuts and kneading in 3/4 cup of semisweet chocolate chips at the same time. Pat the dough into a 9-inch diameter circle on a baking sheet. With a serrated knife, cut into 8 wedges. Bake for 20 to 22 minutes, or until a cake tester or toothpick inserted into the center of a scone comes out clean. Cool as above and recut into wedges, if necessary.