For cupcakes: Preheat oven to 300°F. Line 2 muffin tins with cupcake liners. Whisk together 3 1/4 cups flour, 1 1/2 cups granulated sugar, 1 Tbsp baking powder, 1/4 tsp baking soda and 1/4 tsp salt. In a large bowl, beat 1 cup room-temperature buttermilk, 1/2 cup canola oil, 3 Tbsp St-Germain elderflower liqueur and 5 large egg yolks. Slowly beat in 1 cup unsalted butter, melted. Add fl our mixture, beating on low speed to combine. Place 2 large egg whites in a clean bowl. Using a beater with whisk attachment, beat whites until foamy. Gradually add 1/4 cup granulated sugar, beating until soft peaks form. Fold egg whites into batter. Fill each cupcake liner three-quarters full. Bake 25 minutes or until a toothpick comes out clean. Cool in pans 5 minutes. Remove from pans; cool completely on wire rack.
For frosting: Beat 1 1/2 cups unsalted butter, softened, and 1 1/2 lb (6 cups)confectioners' sugar in a large bowl. Beat in 1/4 cup St-Germain elderflower liqueur, 2 Tbsp milk and 2 tsp vanilla extract. Spread or pipe frosting evenly over cupcakes.Makes 24 cupcakes.
ST-G CHAMPAGNE COCKTAIL
Pour 2 oz St-Germain elderflower liqueur in a champagne flute. Top with 3 oz sparkling wine; garnish with lemon twist. Serves 1.