- Preheat oven to 325 degrees. Grease and line a sheet pan with parchment paper. Set aside.
- Melt white chocolate over a water bath on low. Once melted, remove from heat. Allow to cool.
- Mix butter in, a little at a time, until it is completely melted and incorporated with white chocolate.
- In a separate bowl, whisk egg yolks a bit and then mix into white chocolate.
- In a mixing bowl of standing mixer fitted with a whisk attachment, begin whipping egg whites, adding sugar a little at a time. Whisk to soft peaks.
- Fold cake flour into egg whites, followed by white chocolate base. Pour batter into prepared sheet pan and bake for 15−20 minutes, or until cake is cooked through. Allow to cool before cutting.
- For compote, mix cornstarch and cold water together in a small cup. Combine strawberries and sugar and allow them to macerate in a small saucepan for 5 minutes. Cook strawberries on low, reducing liquid. Once most liquid is gone, add Grand Marnier and cornstarch-water mixture. Cook until compote has thickened, about 2−3 minutes. Refrigerate until needed
- For diplomat cream, combine milk, vanilla extract, ¼ cup sugar, and vanilla bean seeds in a pot and bring to a boil. Whisk together other ¼ cup sugar and egg yolks, then add cornstarch. Temper eggs with hot milk mixture. Return mixture to pot and cook until custard is thick and large bubbles rise up. Take custard off heat. Whisk in gelatin, then allow it to cool. Slowly add butter into custard (use immersion blender to emulsify if necessary). Strain and refrigerate with plastic wrap directly on the surface to prevent a skin from forming.
- To finish diplomat cream, whisk heavy cream in a mixing bowl fitted with whisk attachment. Whisk until firm peaks form. Fold into cold pastry cream and keep refrigerated until assembly.
- When ready to assemble, cut cooled cake in half. Spread the strawberry compote on bottom layer, followed by diplomat cream. Place second cake on top. Pipe or spread vanilla whipped cream* on top of cake, if desired.
*Chef Watkins makes her own vanilla whipped cream with 1¼ cups heavy cream, ½ cup powdered sugar, and one scraped vanilla bean.