Preheat oven to 350. Grease 9×9 baking pan. (You can use an 8×8; the blondies will just be slightly taller.)
Into a large mixing bowl, sift together: 1 c. all-purpose flour, ½ tsp baking powder, 1/8 tsp baking soda, and ½ tsp salt.
In a large bowl, beat together 1 c brown sugar with 1 stick melted butter. Add 1 large egg and ¼ tsp vanilla.
Stir the flour mixture into the butter mixture along with 1 c. coarsely chopped Heath bars. (Add nuts if you feel so inspired, but don’t tell me about it. I hate nuts in cookies and brownies). Pour batter into pan.
Bake for 20 to 25 minutes. Let cool (if you have the patience) before cutting into squares.