Preheat oven to 350F and line an 8x8 baking pan with parchment paper.

To make batter, whisk melted butter, brown sugar, pumpkin puree, eggs and vanilla extract together in a large mixing bowl. In a separate bowl combine flour and pumpkin pie spice. Fold dry ingredients into wet with a flat spatula.

Pour batter into the prepared pan and spread into an even layer.

Mix swirl ingredients with a fork until evenly combined - this mixture should be slightly crumbly.

Pour over the top of the batter and swirl the crumble into batter with a toothpick or clean knife.

Place in the oven and bake for 40 minutes. Allow to cool completely before cutting into squares.