Start by warming 1 cup of whole milk and 1/4 cup of unsalted butter in a saucepan until the butter melts. Remove from heat, add 2 teaspoons of instant yeast and 1/4 cup of granulated sugar, stir gently, and let sit for 5 minutes until frothy.

In a stand mixer bowl, combine the milk mixture with 1 large beaten egg, 3 1/2 cups of all-purpose flour, and 1 teaspoon of salt. Mix on low speed until a rough dough forms, then increase speed to medium for 5-7 minutes until smooth.

Transfer the dough to a greased bowl, cover, and let rise in a warm area for about 1 to 1.5 hours until doubled in size.

Prepare the filling by cooking 2 cups of sliced rhubarb, 1/2 cup of granulated sugar, 2 tablespoons of lemon juice, and 2 tablespoons of cornstarch in a saucepan over medium heat for about 10 minutes until thickened.

Once the dough has risen, punch it down. Roll it out into an 18x12 inch rectangle and spread the cooled filling over the dough.

Starting from one edge, roll up the dough tightly into a log shape, pinch seams, and slice into 12 pieces. Arrange in a greased 9x13 inch pan.

Cover the rolls and let rise again in a warm spot for 30-45 minutes until puffy.

Preheat oven to 350°F. Brush tops with a beaten egg wash and bake for 25-30 minutes until golden.

While baking, prepare the glaze by whisking together 1/2 cup of the reserved rhubarb filling, 1 cup of powdered sugar, and 1 tablespoon of lemon juice.

Once baked, let the rolls cool for 10 minutes, then drizzle with glaze and serve warm.