Grape-Filled Strudel with White Wine Sauce (Szōlōs Rétes Bor Szószban)

Ingredients

• 6 Tbsp. butter, melted
• ¹⁄₃ cup coarse semolina
• 3 (12" × 17") sheets frozen phyllo dough, thawed
• 6 tbsp. dried bread crumbs
• 2 cups seedless black grapes (about 10 oz.)
• 2 egg whites, beaten to soft peaks
• ¹⁄₃ cup granulated sugar
• 1 tsp. vanilla sugar
• ³⁄₄ tsp. ground cinnamon
• 2 Tbsp. honey, preferably acacia
• 1 Tbsp. sour cream
• ³⁄₄ cup sugar
• 3 Tbsp. flour
• 6 egg yolks
• 1 ¹⁄₂ cups milk
• ¹⁄₂ cup white wine, preferably riesling
• 1 tsp. lemon zest