Preheat the oven to 180C & grease & line a 9 x 9-inch brownie tin with baking parchment; set aside.
First, make the crust. Place the butter in a saucepan over a medium to high heat & leave to brown. Swirl the butter occasionally. After about 5 minutes, the foam should subside & you should start to see a light brown colour, & it should smell nutty. Remove from the heat & pour into a different bowl to cool to room temperature. (I’m impatient, so our butter was promptly put into the fridge to cool down.)
In a large bowl, combine the flour with the brown sugar. Pour in the cooled brown butter & mix until a ball of dough forms. Neatly press the dough into the prepared tin until evenly dispersed & bake in the preheated oven for about 20 minutes, or until lightly golden. Set aside to cool.
Next, make the crisp topping. Using your fingertips, combine all of the ingredients in a large bowl until crumbs start to form. Set aside.
Now the filling. Place all of the ingredients in a large bowl and whisk to combine. Once smooth, pour over the par-baked crust and bake in the oven for 15-minutes.
After 15-minutes, remove the pumpkin bars from the oven and gently sprinkle the crumble evenly over the top. Return the bars to the oven for a further 20-25 minutes, until the middle still has a slight jiggle and the crumble is a golden brown.
Leave to cool in the tin for 15 minutes before moving to a wire rack to cool completely.
Cut into squares and serve with lightly whipped cream. Enjoy!