Begin by bringing all your ingredients to room temperature. Preheat the oven to 350F/177C convection (325F/163C conventional) and grease and line three 6 inch cake pans.
In a medium bowl, whisk together the flour, cocoa powder, baking powder and salt until they're evenly distributed.
1 3/4 cups (210)g all-purpose flour spooned and leveled, 3/4 cup (60g) cocoa powder spooned and leveled, 1 Tbsp (10g) baking powder, 1/2 tsp salt
Place the room temperature butter, the oil and the granulated sugar in a large bowl and use an electric mixer with the whisk attachment to beat them for 2 minutes.
1/4 cup (56g) unsalted butter room temperature, 1/2 cup (118mL) canola oil, 1 1/2 cup (300g) granulated sugar
Add the eggs, one at a time, beating on medium speed until each egg is fully incorporated. Add the sour cream and beat just until it's combined.
3 large eggs room temperature, 3/4 cup (170g) sour cream
Add half of the dry ingredients to the batter, turn the mixer on low speed and then pour in the milk, followed by the rest of the dry ingredients.
3/4 cup (180mL) milk room temperature
Distribute the batter evenly among the three cake pans, about 14oz in each pan and bake for 30-35 minutes. When the cake is fully baked it will release itself from the edge of the pan and it will spring back if you press on the center of it.
Allow the cake to cool in the pan for 5 minutes and then invert them onto a tea towel or cooling rack. Then allow them to cool completely before frosting.
