Prep the oven and pan: Preheat to 350°F (175°C). Line a 12-cup muffin tin with high-quality liners.
Set aside.
Mix dry ingredients: In a large bowl, whisk flour, sugar, baking powder, baking soda, and salt until evenly combined.
Combine wet ingredients: In a separate bowl, whisk melted butter, eggs, milk, sour cream, and vanilla until smooth.
Make the batter: Pour wet ingredients into dry and whisk gently until just combined. Do not overmix. The batter should be smooth but not runny.
Fill the liners: Divide the batter evenly among cups, filling about two-thirds full for level tops.
Bake: Bake 16–19 minutes, or until the centers spring back and a toothpick comes out clean or with a few moist crumbs.
Cool completely: Let cupcakes cool in the pan for 5 minutes, then transfer to a rack to cool fully before frosting.
Make the buttercream: In a mixer bowl, beat butter on medium-high for 2 minutes until pale and fluffy.
Add powdered sugar 1 cup at a time on low, then beat on medium until smooth. Mix in vanilla bean paste, salt, and 2 tablespoons cream. Add more cream if needed for a creamy, pipeable texture.
Frost: Fit a piping bag with a large star tip.
Fill with buttercream and pipe tall swirls or rosettes. Smooth with an offset spatula if you prefer a modern flat-top look.
Decorate: Finish with pearls, a touch of gold leaf, or a single edible flower petal for an elegant, modern style.