Cupcakes
2 sticks unsalted butter, softened
2 cups sugar
4 eggs
3 cups all-purpose flour
1/2 tsp. baking soda
1/2 tsp. salt
1 cup milk
2 Tbsp. lemon zest
2 Tbsp. lemon juice

Frosting
4 oz. (1 stick) unsalted butter, softened
2 3/4 cups powdered sugar
1/2 tsp. salt
1 Tbsp. plus 1 tsp. whole milk
1 tsp. pure vanilla extract
2 Tbsp fresh lemon juice