Preheat your oven to 350°F (175°C) and line a 9 x 9 inch baking pan with parchment paper.

Cream the butter with brown sugar and granulated sugar for about 3 minutes until light and fluffy.

Mix in the eggs and vanilla extract until fully incorporated.

Combine all-purpose flour and remaining dry ingredients in a separate bowl, then add to the wet mixture until just mixed.

Press the dough into the lined baking pan and bake for about 15 minutes until edges are golden brown.

Prepare the filling by whisking together pumpkin puree, heavy cream, eggs, both sugars, cornstarch, pumpkin pie spice, and salt until smooth.

Pour the filling over the baked crust and bake at 400°F (200°C) for 15 minutes, then reduce to 350°F (175°C) and bake for an additional 40 minutes.

Allow to cool on a wire rack for 45 to 60 minutes, then refrigerate for at least 3 hours or overnight.

Slice into squares and serve, possibly topped with whipped cream and a sprinkle of nutmeg.