Preheat oven to 325°F.
Butter two 6” cake pans and line the bottom of each pan with a piece of round parchment paper cut to fit (optional but highly recommended).
In a small mixing bowl, add flour, salt, baking powder and mix with a whisk to distribute evenly. Set aside.
Add egg, sugar and vanilla extract to the bowl of a stand mixer and beat until light and creamy, about 2 minutes. Add the flour mixture and stir until just combined.
Heat the milk in the microwave for 40 - 50 seconds, add butter and oil to the hot milk and stir until the butter is completely melted. Add milk mixture to the stand mixer bowl while stirring to combine. Scrape the bowl with a spatula to ensure thorough mixing.
Divide batter evenly between the 2 prepared cake pans, about 280 g of batter per pan.
Bake in the middle oven rack for 20 - 25 minutes until a toothpick inserted in the middle of the cake comes out clean.
Remove from the oven and allow to cool to the touch. Run a paring knife along the edge to loosen the cakes if necessary and remove them from the pan. Peel off parchment paper if using and allow to cool completely on a wire rack.