01 -
Preheat oven to 350 degrees Fahrenheit.
02 -
Cream granulated sugar and softened butter with a stand or hand mixer on medium speed until light and fluffy. Add eggs one at a time, fully incorporating each before adding the next. Mix in vanilla extract thoroughly.
03 -
Whisk together the all-purpose flour and baking powder. Reduce mixer speed to low and gradually blend the flour mixture into the wet ingredients until combined without overmixing.
04 -
Evenly spread half of the cookie batter into an ungreased 15×10 inch jelly roll pan. Spread the blackberry pie filling evenly over the batter layer. Drop the remaining batter by spoonfuls over the filling, distributing as uniformly as possible.
05 -
Bake in the preheated oven for 45 minutes or until the top is golden brown. Avoid underbaking. Remove from oven and transfer the pan to a wire rack to cool slightly.
06 -
Combine powdered sugar, melted butter, and 2 to 3 tablespoons of fresh lemon juice in a small bowl, adjusting lemon juice to achieve a drizzleable consistency.
07 -
Drizzle the lemon glaze evenly over the warm bars. Allow to cool completely on the wire rack before slicing into 16 squares.