I preheat the oven to 350°F (175°C). I line an 8x8-inch pan with parchment paper, leaving overhang for handles, and spray with cooking spray for easy removal of these apple crumble squares.

I beat ½ cup softened butter and ¼ cup brown sugar until fluffy, about 2–3 minutes. I add ½ tsp vanilla extract and 1 ¼ cups flour, mixing until crumbly, then press evenly into the pan for a solid Fall Dessert Bars base.

I bake the base for 12–14 minutes until slightly puffed, keeping the oven at 350°F, setting a sturdy foundation for these autumn crisp treats.

I peel, core, and slice 4 cups apples into ¼-inch pieces. In a bowl, I toss them with 2 tbsp flour and ¼ cup granulated sugar, then spread evenly over the baked base for these Apple Crisp Bars.

In a bowl, I mix ½ cup brown sugar, ¼ cup granulated sugar, ¾ cup flour, ½ cup oats, 1 tsp cinnamon, and ½ tsp salt. I cut in 6 tbsp cold butter until pea-sized crumbs form, then sprinkle over the apples for crisp apple crumble squares.

I bake for 45 minutes until the topping is golden and apples are bubbly. I cool completely in the pan, then lift out using parchment handles and cut into 16 bars for perfect Apple Crisp Bars.