Preheat the oven: Preheat the oven to 356ºF (180ºC). Line a round 9-inch baking pan with parchment paper and set aside. Note: Alternatively, if you have a non-stick pan, liberally grease it with softened/spreadable butter and dust it with a light layer of flour. This will leave your finished cake with smooth sides.
Combine dry ingredients: In a large mixing bowl, add flour, baking powder, baking soda, and salt. Whisk until well combined. Add sugar: Whisk through the sugar.
Add wet ingredients: Pour in milk, yogurt, oil, vinegar, and vanilla. Mix batter: Gently fold with a spatula until just combined, about 40 seconds. Avoid over-mixing, the batter should be smooth with no visible flour streaks.
Pour into pan: Transfer the batter to the prepared tin and smooth out the top.
Bake: Bakefor 35–40 minutes or until a toothpick inserted into the center comes out clean or with a few moist crumbs. Remove from the oven and let the cake cool in the pan for 15 minutes.
Remove & Cool: Carefully remove from the pan and transfer to a wire rack to cool completely before adding the frosting.
Buttercream Frosting
Beat Butter: In a large mixing bowl, beat the softened butter on medium-high speed for 30 seconds until creamy.
Add remaining ingredients: Add the powdered sugar, milk, and vanilla. Beat on high speed until well combined, creamy, and fluffy, about 30 seconds, adding more milk if it’s too dry, 1/2 tablespoon at a time.
Frost the cake: Spread the buttercream frosting over the cooled cake.
Set and serve: Let the frosting set for about 20 minutes. Slice into triangles and enjoy!
Notes
Store: Keep in an airtight container at room temperature for 3–4 days, or refrigerate for up to 5 days.Freeze: Wrap individual slices in plastic wrap and foil. Freeze for up to 3 months.Thaw: Defrost at room temperature or overnight in the fridge before serving.