01 - Generously grease a 10-inch bundt pan or tube pan with butter or nonstick spray.
02 - In a large mixing bowl, combine warmed milk, 1/4 cup granulated sugar, and active dry yeast. Allow mixture to sit for 5–10 minutes until foamy.
03 - Add melted butter, eggs, and salt to the yeast mixture. Whisk until well incorporated.
04 - Gradually add all-purpose flour to the wet mixture, stirring until a soft dough forms. Knead by hand or with a stand mixer for 5–7 minutes, until the dough is smooth and elastic.
05 - Gently knead in 1/3 cup rainbow sprinkles until evenly distributed throughout the dough.
06 - Transfer dough to a lightly greased bowl. Cover and let rise in a warm, draft-free area for 60–75 minutes, until doubled in volume.
07 - While dough rises, mix 1/2 cup granulated sugar and 1 tablespoon ground cinnamon in a small bowl for the coating.
08 - In a separate bowl, combine 1/2 cup flour, 1/4 cup brown sugar, cold cubed butter, 1/4 teaspoon cinnamon, and pinch of salt. Work mixture with a fork until crumbly. Chill streusel until ready to use.
09 - Punch down the risen dough. Pinch off 1-inch pieces and roll each into a ball.
10 - Dip each ball into melted butter and roll in the cinnamon sugar mixture, ensuring even coverage.
11 - Arrange coated dough balls evenly in the prepared pan, building layers as needed.
12 - Sprinkle the chilled streusel topping evenly over the dough balls.
13 - Cover the pan and let the dough balls rise for 30 minutes, until puffy.
14 - Preheat oven to 350°F. Bake for 35–40 minutes, until golden brown and set. Allow to cool in the pan for 10 minutes, then invert onto a wire rack.
15 - Whisk together 1 cup powdered sugar, 2–3 tablespoons milk, and vanilla extract until smooth.
16 - Drizzle the glaze over the warm bread and garnish with additional rainbow sprinkles. Serve while warm.