For cookie filling, stir together the peanut butter, powdered sugar, 2 tablespoons of butter and vanilla until well mixed. Set aside.
Brush 1 sheet of phyllo dough with some of the melted butter. (Keep remaining sheets covered with a damp towel to prevent them from drying out.) Cut phyllo sheet lengthwise into 4 long strips. Place a slightly rounded teaspoon of the peanut butter filing about 1" from one end of one of the strips. Starting at the same end with the filing, fold a corner of the dough over the filling so it lines up with the other side of the strip, forming a triangle. Continue folding like a flag in a triangular shape, using the entire strip. Repeat with the remaining cut strips and sheets of phyllo. Brush each triangle with melted butter and place on an ungreased cookie sheet, seam side down. Bake in a 400 oven for 6 to 8 minutes or until golden. Cool on wire racks.
Pipe or drizzle the tops of the triangles with melted chocolate (thin chocolate with melted shortening, if necessary). Or, if desired, spread cookies with chocolate and sprinkle with chopped pecans. Cool until chocolate sets. Serve immediately or cover and chill for up to 2 days. Makes 28.
You can freeze the UNFROSTED triangles to have on hand for last minute holiday entertaining or gift giving. Decorate with chocolate and nuts just before serving.