Chocolate cake

Ingredients
1 1/2 cups (300g) granulated sugar
1/2 cup (110g) packed light-brown sugar
3/4 cup (70g) unsweetened cocoa powder (scoop and level to measure)
1 tsp baking soda
3/4 tsp salt
1 cup (235ml) boiling water*
3/4 cup (175ml) vegetable oil or canola oil
1/4 cup (56g) unsalted butter, melted
2 large eggs
3 large egg yolks
1 Tbsp vanilla extract
2 cups (256g) all-purpose flour (spoon and level to measure)
1/2 cup (116g) sour cream
1/3 cup (80ml) milk
1 recipe Chocolate Buttercream Frosting
Instructions