Coffee-Walnut Cake with Coffee-Mascarpone Cream

INGREDIENTS

• 1/2 teaspoon vanilla extract
• 10 tablespoons (1 1/4 sticks) unsalted butter, room temperature
• 1/2 cup (4 ounces) mascarpone cheese*
• 1/2 cup powdered sugar
• 1 cup walnuts (about 4 ounces), toasted, chopped, divided
• 1/4 teaspoon ground cinnamon
• 1/2 teaspoon ground cinnamon
• 2 teaspoons baking powder
• 3/4 cup buttermilk
• 3 large eggs
• 1 cup chilled heavy whipping cream
• 1 cup sugar, divided
• 4 1/2 teaspoons instant espresso powder
• Pinch of salt
• 1/4 teaspoon baking soda
• 1 large egg yolk
• 3/4 cup (about 3 ounces) walnuts, toasted, chopped
• 1 tablespoon instant espresso powder
• 1/4 teaspoon salt
• 1 1/3 cups all purpose flour
• 1 tablespoon water