Heat oven to 325 degrees F. Add cupcake liners to muffin tins. In a medium-sized bowl, mix flour, baking powder, baking soda and salt. Set aside.
In the bowl of a stand mixer (or can use a large mixing bowl and an electric hand mixer), add butter and sugar. Cream butter until light and fluffy using the paddle attachment. On slow speed, add eggs, one at a time and until completely mixed. Then, add vanilla extract and vegetable oil and mix.
Add dry ingredients and mix on slow speed until incorporated. Do not overmix. Add milk and mix on slow speed for 30 seconds. Scrape bottom and mix again for 20 to 30 second or until batter is smooth.
Scoop or pour 1/4 cup batter into each cupcake liner. Bake 20 to 22 minutes or until a toothpick in center comes out clean. Remove cupcakes from muffin tin and allow to cool on cooling rack.
Vanilla Buttercream
In the bowl of a stand mixer, add butter and beat with paddle attachment until smooth. Add powdered sugar in two batches and mix until creamed. Add vanilla and mix.
Add milk, gradually, starting with half. Mix and and continue adding milk until smooth. Continue mixing buttercream for 4 to 5 minutes. Store in the refrigerator if not using immediately. Place buttercream on your kitchen counter for at least 15 to 20 minutes before using (if refrigerating).
Notes
Freezing Tips
The baked cupcakes freeze really well. Make sure they are completely cooled and place in a freezer-safe zippered plastic bag (do not stack them) and freeze them until you're ready to eat. Defrost in your refrigerator overnight and then leave them on your counter (still sealed) until they are room temperature. Decorate with frosting and serve.
Buttercream recipe from Saint Cupcake. Vanilla Cupcakes from The Little Kitchen.