Plum Yeast Cakes (Kuchens)

Ingredients

• 3/4 cup lukewarm milk
• 1 Tbsp active dry yeast
• 1/4 cup sugar
• 3 cups flour
• 1 tsp salt
• 2 large eggs
• 6 Tbsp unsalted butter, softened
• 1 cup heavy cream
• 3/4 cup sugar
• 1 tsp cornstarch
• 1/4 tsp salt
• 1 large egg PLUS 1 large egg yolk
• 1 Tbsp unsalted butter
• 1 tsp pure vanilla extract
• 4 plums, sliced 1/4-inch thick
• cinnamon for sprinkling
• sea salt for sprinkling