Preheat oven to 180 °C (350°F) (see note 1 if using a fan function) and grease and/or line two 8 inch cake tins. I use my homemade cake release to grease my tins.

In a bowl, sift together flour, cornstarch, baking soda, baking powder and salt. Using a whisk or fork, mix until well combined. Set aside.

In a large bowl, add in butter, vegetable oil, white granulated sugar, soft brown sugar and peanut butter. Using an electric mixer (hand or stand mixer are both fine - see note 2), cream together on a medium speed for 3 minutes until light and creamy.

Add in eggs one at a time on a low speed, mixing well in between each addition (about 10-15 seconds between eggs).

Add in vanilla and buttermilk, and mix on a medium speed until well combined. You should have a smooth creamy batter. Now set your mixer aside as the remainder of the batter will be finished by hand.

Add in the pre-sifted dry ingredients from earlier and using a spatula, gently fold until just combined. Do not overmix (see note 3).

Distribute the batter evenly into the two 8 inch cake tins, and drop the cake tins lightly on the counter to remove any large air bubbles. Bake for 30-35 minutes or until a toothpick comes out clean or with a few moist crumbs on it.

Once baked, allow the cakes to cool in the cake tins for about 15-20 minutes, and then turn them out onto a wire rack to completely cool before frosting with the peanut butter frosting.

Before beginning: If you're making a simple cake with no crumb coat, only a thin layer of frosting on the sides and little to no piping, you can get away with making a half batch (or ¾s) of the frosting :)

In a large bowl (or in the bowl of a stand mixer if using one), add in butter, powdered sugar, vanilla, cream, peanut butter and salt.

Mix on the lowest speed until the ingredients are combined (about a minute), and then turn up the speed to a medium high and mix for a full 10 minutes, scraping down the bowl half way through. If using a stand mixer then use the paddle attachment.

The frosting should be silky smooth and it's now ready to use! See note 4 if your frosting isn't light and smooth, or too soft.