Shortbread base:
1 1/2 sticks unsalted butter
2 cups all-purpose flour
1/2 cup packed light brown sugar
1/2 tsp salt
Preheat oven to 350F. Line a 13 x 9-inch pan with quick release aluminum foil.
Mix dry ingredients in a medium mixing bowl. Add room temperatur butter and mix. The original recipe did this in a food processor. I prefer to mix it with my hands until the ingredients are well combined. Then sprinkle the mixture in the pan and press evenly over the bottom of the pan. Bake shortbread in middle of oven until golden, about 20 minutes.
While shortbread is baking, prepare topping.
