Knead all dough ingredients, cover, and let rise for 1 hour.
Cook diced apples, sugar, and cinnamon in butter. Add cornstarch mixed with water, cook until thick. Cool.
Mix cream cheese, sugar, and vanilla sugar.
Divide dough into 9 balls. Flatten centers, fill with cheesecake and apple filling, then top with streusel. Brush edges with egg yolk.
Bake at 180°C (356°F) for 20-25 minutes. Drizzle with glaze.
