1 3/4cupscake flour, spooned and levelled *see Note 1 below for DIY cake flour tip
1 1/2teaspoonsbaking powder
1/2teaspoonbaking soda
1/2teaspoonfine salt, a bit less if using salted butter
1/4cupunsalted butter, at room temperature
2largeeggs, at room temperature
1/3cupfull-fat sour cream
1/4cupcanola, vegetable or other neutral tasting cooking oil, vegetable or other neutral tasting cooking oil
1Tablespoonpure vanilla extract, or vanilla bean paste
2/3cupwhole milk, 3%
Frosting:
1cupunsalted butter, at room temperature
4cupsicing/confectioners' sugar
1teaspoonvanilla extract, optional
3-4Tablespoonsmilk
Food colouring, for colouring frosting, if desired
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Instructions
Preheat oven to 350F. with rack in centre of oven. Prepare 16 muffin cups with paper liners and set aside.
In a large bowl with an electric mixer, or the bowl of a stand mixer fitter with a beating blade, mix together the sugar, flour baking powder, baking soda and salt. Add the butter and mix on medium-low speed for 3 minutes. Mixture will be fine crumbs at that point.
In a small bowl, whisk together the eggs, sour cream, oil and vanilla. Add the egg mixture to the flour mixture and beat on medium speed until just combined. Slowly add the milk and mix on low speed until just combined. Do not overmix. Batter will be quite liquid.
Fill muffin liners with batter about 1/2 to no more than 2/3 full. You should get 16 cupcakes.
Bake in preheated oven 14-16 minutes, or until a tester inserted in the centre comes out clean.
Immediately remove cupcakes from muffin tins and allow to cool completely on a cooling rack before frosting.
For frosting: Beat room temperature butter in a medium bowl with an electric mixer or in a stand mixer with a beater blade for 2-3 minutes. Turn mixer off. Add icing sugar, vanilla (if using) and 3 Tbsp of milk. Turn mixer on low and mix until sugar is incorporated. Increase mixer speed to medium to thoroughly combine and judge consistency. If necessary, add more milk in very (very!) small increments and continue mixing on medium until frosting looks smooth and creamy. Add food colouring, if desired. Beat frosting for and addition 2 minutes on high speed until fluffy.
Notes
How to make your own cake flour: If you find yourself without cake flour, simply remove 2 Tablespoons of flour from one cup of all purpose flour and replace it with two Tablespoons of cornstarch (corn flour). For this recipe specifically, measure out 1 3/4 cups of all purpose flour and remove 2 Tablespoons plus 2 teaspoons of flour and replace with the same amount of cornstarch.