Heat the oven to 325°F and fit paper liners into the cupcake pan. The liners should sit flat in the wells so the batter can rise evenly.

Simmer 1 1/2 cups pink champagne in a saucepan for about 6–8 minutes, checking for a final volume of 3/4 cup, then cool it to room temperature and set aside 1–2 Tablespoons for frosting. The finished reduction should remain pourable, with gentle bubbling during cooking rather than a thick, sticky syrup.

Whisk the flour, baking powder, and salt together in a small bowl. An evenly blended dry mixture distributes the leavening throughout the batter.

Work the salted butter and vanilla together with an electric mixer until the mixture becomes creamy. Look for a uniform texture with no firm butter pieces, and a slightly lighter appearance as the mixer incorporates air.

Mix the sugar, vegetable oil, and eggs into the butter mixture until evenly combined. The mixture should look cohesive rather than showing separate pools of oil.

With the mixer at medium speed, add the flour mixture and remaining cooled reduction in alternating portions, letting each nearly blend before the next and scraping the bowl’s sides and base as needed. Stop once the batter looks uniform, without dry pockets or flour streaks, to avoid unnecessary mixing.

Portion the batter into the liners to 3/4 full and bake for 18–20 minutes. A toothpick inserted into the center should come out without wet batter, though a few moist crumbs are fine.

Whip the room-temperature unsalted butter, confectioners sugar, vanilla, and 2 Tablespoons of reserved champagne reduction with an electric mixer, adding milk as needed for the desired consistency. The buttercream should develop a soft satin sheen and hold a ridge when you lift the beater, without looking runny or grainy.