"Thousand Layer" Chocolate Brioche

Ingredients

• 6 tablespoons unsalted butter, very soft
• 3 large eggs, beaten
• 1 package active dry yeast
• 0.75 cup warm whole milk
• 0.33 cup white granulated sugar
• 4 tablespoons unsalted butter for laminating dough
• 1 teaspoon fine salt
• 1 large whole egg for brushing
• 0.5 cup dark chocolate chunks
• white granulated sugar
• coarse sea salt
• 4.5 cups all-purpose flour