Chocolate Walnut Povitica

Ingredients

• 3 tablespoons plus 1/2 teaspoon sugar, divided
• 2 cups plus 1/4 teaspoon all purpose flour, divided
• 2 tablespoons warm water
• 1 1/2 teaspoons active dry yeast
• 1/2 cup milk
• 1 teaspoon salt
• 1 egg
• 1 teaspoon vanilla extract
• 1 tablespoon unsalted butter, melted
• 1 1/2 cups walnuts
• 1/2 cup granulated sugar
• 2 tablespoons unsweetened cocoa powder
• 1/4 cup milk
• 1/4 cup unsalted butter
• 1 egg yolk, beaten
• 1 teaspoon vanilla extract
• 1 egg white, lightly beaten
• sugar