Blueberry Croissant Recipe

Name: Blueberry Croissant Recipe
Ingredients: 3 cups All-purpose flour; 1/4 cup Granulated sugar; 1 tsp Salt; 2 1/4 tsp Active dry yeast (1 standard packet); 3/4 cup Warm milk (~110°F); 1 Large egg (Beaten); 1 cup Unsalted butter (Cold, for lamination); 1 1/2 cups Fresh blueberries (Use 1 1/4 cups if using frozen); 3 tbsp Granulated sugar; 1 tbsp Cornstarch; 1 tsp Lemon zest (Fresh); 1/4 tsp Vanilla extract; 1 pinch Salt; 1 Egg (Beaten, for egg wash); 2 tbsp Coarse sugar (For sprinkling)