In a stand mixer, combine 4 cups of all-purpose flour, 1 cup of whole milk, 1 cup of active sourdough starter, ½ cup of granulated sugar, 2 large eggs, 1 teaspoon of salt, and 1 tablespoon of vanilla extract. Mix on low until everything is integrated, forming a shaggy dough.

Add 4 tablespoons of softened butter to the dough mixture. Knead on medium speed for about 10 minutes until the dough becomes smooth and elastic.

Gently fold in ½ cup of colorful sprinkles using a spatula, ensuring they are evenly distributed throughout the dough.

Transfer the dough into a greased bowl and let it rise in a warm spot for 4-6 hours or until it doubles in size.

Gently deflate the dough, shape it into a loaf form, and place it into a greased loaf pan, seam-side down.

Cover the shaped dough again and allow it to rise for an additional 2-3 hours until it feels airy.

Preheat your oven to 375°F (190°C) about 30 minutes before baking.

Bake the loaf for 30-35 minutes until the top is a golden brown and sounds hollow when tapped.

Let the loaf cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.