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, baking powder and salt until they're evenly distributed.
2 1/4 (270g) cups all-purpose flour, 1 Tbsp (10g) baking powder, 1/2 tsp salt
Place the room temperature butter, oil and granulated sugar in a large bowl and use an electric mixer with the whisk attachment to beat them for 2 minutes.
1/4 cup (60g) unsalted butter, 1/2 cup (120mL) 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 vanilla extract and beat just until combined.
3 large eggs, 3/4 cup (170g) sour cream, 1 Tbsp vanilla extract
Add half of the dry ingredients to the wet ingredients, 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
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.
Invert the cakes onto a tea towel or cooling rack and allow the cake to cool completely before frosting.