Preheat your oven to 350°F. Line a standard, 12 count muffin tin with paper liners, and set aside.
Make the cupcakes: In a medium bowl, combine flour, baking powder, and salt. Whisk to combine, and set aside to prep the wet ingredients.
In a large bowl, combine butter, oil, and sugar. Beat together until they're incorporated (some small clumps are fine). Add your egg, sour cream, and vanilla extract. Whisk to combine.
Combine the wet and dry ingredients. Mix together until just combined. Again, some lumps are fine! Add the sprinkles to the batter, and mix until incorporated. Take care not to over mix as it can cause the cupcakes to end up tough and the sprinkles may start to bleed into the batter!
Fill each muffin cup with batter (no more than 3/4 of the way full). Bake in the center of your preheated 350°F oven for 18 to 20 minutes, or until a skewer inserted into the center comes out clean. Cool completely to room temperature before frosting.
Make the buttercream frosting: In a large bowl, combine butter and powdered sugar. Using an electric mixer fitted with the paddle attachment, beat the butter and sugar together for 3 to 4 minutes, or until the sugar is fully dissolved and the mixture is smooth and fluffy.
Add your salt, vanilla, and 2 tablespoons of milk or heavy cream. Beat the mixture again for another 1 to 2 minutes, or until light and airy. Gradually add more milk/heavy cream if needed to reach your desired consistency.
Pipe or spread your frosting onto the cooled cupcakes. (Optional) Top with more sprinkles of your choice! (Not optional) Celebrate!