In a saucepan over medium heat, melt 1/4 cup butter. Stir in powdered sugar and corn syrup until dissolved. Bring to a gentle boil, stirring constantly.
Add pecans, mix well, then refrigerate filling for 30 minutes to thicken.
Meanwhile, preheat oven to 350°F (175°C). Grease a mini muffin pan.
In a bowl, sift together flour and baking powder; set aside.
In a separate large bowl, beat brown sugar and softened butter until light and fluffy.
Add egg and vanilla extract; beat until well combined.
Gradually stir in the flour mixture to form a soft dough.
Roll dough into 1-tablespoon-sized balls and press each into the muffin pan to form a cup.
Spoon about 1 teaspoon of chilled pecan filling into each dough cup.
Bake for 10–13 minutes, or until cookie edges are lightly golden.
Let cool in the pan for 5 minutes before transferring to a wire rack.