Warm up the milk in a heatproof bowl (microwave for 20-30 seconds).
In a stand mixer with a dough hook, combine warm milk, instant dry yeast, and granulated sugar. Stir on low to mix.
Add melted butter, vanilla extract, and eggs. Mix on low.
Gradually add flour and salt while mixing on low for 5 minutes.
Fold in the sprinkles until just mixed. Place the dough in an oiled bowl, cover, and let it rise in the oven (off) for 1 hour.
**For the filling:**
Mix softened butter, brown sugar, cinnamon, vanilla, and salt in a bowl. Set aside.
**For assembly:**
Grease and line a 9×13 inch baking pan with parchment paper.
Roll out the risen dough on a floured counter into a 20×14 inch rectangle.
Spread the butter mixture over the dough, leaving a ¼ inch margin.
Roll the dough into a log and cut into 12 rolls. Place them in the baking pan.
Cover and let them rise for 30-45 minutes. Preheat the oven to 350°.
Pour ¼ cup heavy cream between the rolls. Bake for 20-25 minutes.
For the frosting, mix soft butter, vanilla, salt, and powdered sugar. Adjust consistency with heavy cream or milk.
Spread the frosting on the rolls and top with extra sprinkles. Enjoy!
Notes
To make them the night before, follow the steps until cutting the rolls. Refrigerate covered for up to 24 hours. Allow to come to room temperature for 1 hour before baking. Then, follow the baking and frosting instructions for a delicious treat!