Preheat the oven to 350°F (180°C). Grease an 8x8 inch baking dish lightly and line it with parchment paper.

Cream together the room-temperature butter and white granulated sugar on high speed for 2 minutes until smooth and fluffy.

Sift in the plain flour, cinnamon, nutmeg, and salt to the creamed butter mixture. Mix on low speed until crumbly.

Press the mixture evenly into the prepared baking dish. Bake for 15-20 minutes until lightly golden.

Whisk together the eggs, brown sugar, maple syrup, heavy cream, vanilla extract, and a pinch of salt until light and foamy.

Once the crust cools slightly, sprinkle chopped walnuts over it. Pour the egg mixture evenly over the walnuts.

Return to the oven and bake for another 30-35 minutes until the filling is set and jiggles slightly.

Allow the bars to cool completely in the pan on a wire rack. Lift out using parchment and cut into squares.