Preheat Oven and Prepare Pan: Preheat oven to 350°F (180°C). Grease and flour a 9×9-inch square baking pan and set aside.
Mix Dry Ingredients: In a large mixing bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
Mix Wet Ingredients: In a medium bowl, whisk together sugar, melted butter, olive oil, water, vinegar, and vanilla extract until smooth.
Combine Wet and Dry: Pour the wet mixture into the dry ingredients. Gently fold with a spatula until just combined — do not overmix.
Bake: Pour batter into the prepared pan and bake for 30–32 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Cool: Let the cake cool in the pan for 15 minutes, then transfer to a wire rack to cool completely.
Vanilla Buttercream Frosting
Beat Butter: In a large mixing bowl, beat the softened butter for 2 minutes until creamy.
Add Sugar Gradually: Gradually add powdered sugar, half a cup at a time, beating well (about 15 seconds) after each addition.
Add Milk and Vanilla: Add the water, vanilla extract and salt and then beat for 40 seconds until the frosting is light and fluffy.
Frost Cake: Once the cake is completely cooled, spread the vanilla buttercream frosting evenly over the cake.
Serve: Cut into squares and serve. Enjoy your moist vanilla cake!
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Notes
Store: Keep your cake in an airtight container at room temperature, where it will stay fresh for up to three days.Freeze: You can freeze the cake by wrapping it tightly in plastic wrap or aluminum foil, and placing it in a freezer-safe bag or container. Freeze for up to 3 months.Thaw: When ready to serve, thaw the cake in the refrigerator overnight or for several hours at room temperature until soft.