Break chocolate into 8 equal pieces. Preheat oven to 375F. 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 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 in. to 3-in. 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 round. 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 17-19 minutes, or until lightly browned.
Remove the baking sheet to a wire rack and cool 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.
VARIATION Make the dough as above, omitting bittersweet chocolate, substituting 1/2 c. unsalted peanuts for the chopped peanuts and kneading in 3/4 c. semisweet chocolate chips at the same time. Put the dough into a 9-inch diameter circle on a baking sheet. With a serrated knife, cut into 8 wedges. Bake 20-22 minutes, or until a cake tested or toothpick inserted into the center of a scone comes out clean. Cool as above and recut into wedges, if necessary.