Using a mixer, cream together brown sugar and butter until smooth.
Add egg and vanilla and mix until fully incorporated.
Add flour and baking powder and beat on medium speed until combined.
Chill dough for 30 minutes. While the dough is chilling, heat the oven to 350 F.
After the dough has chilled, shape dough into uniform balls using a 1-oz scoop, placing them two inches apart on ungreased cookie sheets.
Press a well in the center of each cookie to hold the pecan filling. Make sure the well is large enough to accommodate a heaping half tsp of filling. Combine the pecan filling ingredients and stir until mixed.
Place a heaping half-tsp of filling in each cookie well.
Bake for 8 to 12 minutes.
Allow to cool for 2 minutes on the cookie sheets then transfer to racks.