Heat oven to 350°F. Grease and flour two 9- or 8-inch round pans. Place 3/4 cup of the white chocolate chunks in small microwaveable bowl. Microwave on Medium (50%) 1 to 2 minutes or until melted, stirring once halfway through cooking time. Stir until smooth.
In large bowl, combine cake mix, buttermilk, vanilla and egg whites; beat at low speed about 30 seconds to mix. Gradually beat in melted butter. Drizzle melted white chocolate into bowl, beating at medium speed 2 minutes, thoroughly scraping side and bottom of bowl once halfway through beating. Spoon batter evenly into pans.
Bake until tops spring back when touched lightly in center. Bake 9-inch pans 25 to 30 minutes, 8-inch pans 30 to 35 minutes. Cool cakes in pans 10 minutes. Remove cakes from pans; place on wire racks. Cool completely, about 30 minutes.
Meanwhile, place remaining 1 1/2 cups white chocolate chunks in medium microwavable bowl. Microwave on Medium (50%) 3 to 6 minutes or until melted, stirring once halfway through cooking time. Stir until smooth. Cool completely, about 35 minutes.
Place 1 cake layer on serving plate; spread with strawberry jam. Top with remaining cake layer.
In medium bowl, beat cream cheese at medium speed until soft and fluffy. Add cooled melted white chocolate; beat until of soft spreading consistency. Immediately frost side and top of cake. Arrange strawberry halves on top of cake around edge. Store in refrigerator.