1 Mixon orange
3 1/2 cup granulated sugar
2 lbs. rhubarb, trimmed and sliced
1 lb strawberries (about 4 cups), trimmed and chopped, plus sliced strawberries for garnish
4 large egg yolks, room temperature
2 large eggs, room temperature
1 cup whole milk
3 tsp. vanilla extract
3 cup cake flour (not self-rising)
1 tbsp. baking powder
12 tbsp. butter (no substitutions), cut up, room temperature
1 1/4 cup confections' sugar
8 oz. cream cheese, softened
2 cup heavy cream, cold
Into 4-quart saucepan, squeeze juice from orange. Stir in 2 cup granulated sugar. Cook on medium-high until sugar dissolves, stirring. Add rhubarb: cook 5 minutes or until tender, stirring occasionally. Transfer to bowl; cool slightly. Refrigerate, uncovered, 2 hrs. Stir in chopped strawberries; refrigerate.
Preheat oven to 350F. Grease and line bottoms of three 8-inch. cake pans with parchment paper. Grease and flour parchment and sides of pan.
In medium bowl, whisk egg yolks , whole eggs, 1/4 cup milk, and 2 tsp. vanilla until combined. In large bowl, with mixer on low speed, mix flour, baking powder, remaining 1 1/2 cup granulated sugar, and 1/2 tsp. salt; beat in butter and remaining 3/4 cup milk on medium-high speed. Add egg mixture in 3 batches, beating well between additions. Divide batter evenly among pans. Bake 20-30 minutes or until toothpick inserted in center comes out clean. Cool on wire rack 10 minutes. Loosen sides with knife. Invert cakes onto rack; cool completely.
Place 1 cake on plate. Strain liquid from mixture; discard. Spread half of rhubarb on cake, leaving 1-inch border. Repeat with second cake and remaining rhubarb. Top with third cake.
In large bowl, with mixer on high, whisk confectioners' sugar, cream cheese and remaining 1 tsp. vanilla until fluffy. Slowly drizzle in cream. Whisk on high until stiff peaks form.
Cover cake with frosting. Garnish with berries. Serve immediately, or cover with plastic wrap (before garnishing) and refrigerate up to 1 day.
Notes: Bake and freeze up to a month ahead.