Preheat oven to 350°. Spray 3 (8-inch) round light-colored cake pans with baking spray with flour.
In the bowl of a stand mixer fitted with a paddle attachment, beat butter and sugar at medium speed until fluffy, about 4 minutes. Add vanilla extract and orange extract, and beat until combined.
In a medium bowl, whisk together cake flour, baking powder, and salt. Gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating at low speed just until combined after each addition.
In a large bowl, beat egg whites using a mixer fitted with a whisk attachment at high speed until stiff peaks form; gently fold egg whites into batter in thirds. Pour batter into prepared pans.
Bake until a wooden pick inserted in centers comes out clean, 18 to 20 minutes. Let cool in pans for 10 minutes. Invert from pans onto wire racks, and let cool completely. While still slightly warm, brush each layer with ¼ cup Champagne.
Spoon Grapefruit Buttercream into a piping bag fitted with a round decorating tip, and pipe a ring around inside edge on bottom cake layer. Fill center with ½ to ¾ cup Ruby Red Grapefruit Curd. Repeat with remaining cake layers and stack on cake circle or plate. Spread a smooth layer of buttercream on top and sides of cake. Refrigerate until firm, about 1 hour.
Knead fondant until smooth and pliable. Dust work surface with confectioners’ sugar. Roll out fondant into a 14-inch circle. Roll up onto rolling pin and unroll over cake. Smooth top and sides of cake, working outward from center. Trim excess fondant to bottom edge of cake. Brush off any excess confectioners’ sugar.
Roll out additional fondant. Using round cutters in graduated sizes from ½ to 1½ inches in diameter, cut concentric rings. Cut each ring in half.
In a small bowl, stir vodka with enough gold luster dust to form a thin paint. Brush onto rings and let dry. Place gold rings on cake in a decorative pattern, using a small amount of piping gel to adhere.
Notes
*We used Satin Ice Rolled Fondant.
Recipe by Victoria at https://victoriamag.com/champagne-grapefruit-layer-cake-recipe/