Pour yeast evenly over the warm water and let it bloom for 5 minutes.
2. Step
In a bowl, combine cake mix and 2 cups (255 g) of flour, then pour in the yeast mixture. Stir until it starts to come together, then add the sprinkles. Gently knead the dough together into a ball.
3. Step
Cover with a towel and let the dough rise for 1 hour in a warm place.
4. Step
Place dough on a floured surface and sprinkle with remaining ¼ cup (30 g) of flour. Knead until it is no longer sticky (some extra flour may be needed).
5. Step
Roll out the dough into an oval shape and spread butter on one side of the dough. Then, dust with cinnamon, brown sugar, and rainbow sprinkles.
6. Step
Preheat oven to 350˚F (180˚C).
7. Step
Starting at the bottom of the widest end, roll dough and cut into 1½ to 2-inch (4 to 5 cm) pieces and place in a baking dish. Cover with plastic wrap, and rest for 30 minutes. Bake for 15 minutes, or until golden brown.
8. Step
To make the frosting, mix powdered sugar and milk in a bowl until smooth.
