Preheat the oven to 350°F / 175°C and place 12 cupcake liners in baking pans.

Sift or whisk 1 ¼ cups flour, 1 cup sugar, 1 ¾ tsp baking powder, and ½ tsp salt in a large bowl and set aside.

In a separate, large bowl, whisk together ½ cup whole milk, ½ cup sour cream, ¼ cup vegetable oil, ¼ cup apple sauce, and 1 Tbsp vanilla extract.

Pour the dry ingredients into the wet ingredients and whisk until just combined.

Fill the cupcake liners about ⅔ way full. Bake for 19-21 minutes, or until a toothpick comes out with a few moist crumbs.

Let the cupcakes cool for 5 minutes before moving them to a cooling rack to finish cooling. If you want to accelerate the cooling process, pop the pans into your freezer for about 30 minutes.

Beat 1 cup of butter on a medium speed for 30 seconds with a paddle attachment or hand mixer until smooth.

Mix in 1 ½ tsp vanilla extract or vanilla bean paste and ½ tsp salt on a low speed.

Gradually mix in 3 ½ cups of powdered sugar on a low speed. Halfway through add 1 Tbsp of heavy cream to make the frosting easier to mix.

Mix on low for a couple minutes until the ingredients are fully incorporated and the desired consistency is reached. Scrape the sides of the bowl with a rubber spatula as needed.

If the frosting is too thick, add in additional cream (1 tsp at a time). If the frosting is too thin, add in more powdered sugar (quarter of a cup at a time).

Place the buttercream in a piping bag fit with your favorite frosting tip and pipe large swirls onto the fully cooled cupcakes.

Decorated as desired, then enjoy!