Prepare Dough: Heat 1 cup of whole milk and 4 tablespoons of cubed unsalted butter over low heat until warm but not boiling. Stir in 2 1/4 teaspoons of instant yeast and 2 tablespoons of granulated sugar, letting it bubble and foam for about 5 minutes. In a mixing bowl, combine the yeast mixture with 1 large beaten egg, 3 1/4 cups of all-purpose flour, and 3/4 teaspoon of salt. Mix until a dough forms.

Knead Dough: Transfer the dough to a floured surface and knead for about 8-10 minutes until smooth and elastic. Shape the dough into a ball and place it in a lightly greased bowl. Cover the bowl with a clean kitchen towel.

First Rise: Let the dough rise in a warm place until it has doubled in size, approximately 1 to 1.5 hours.

Make Filling: In a medium saucepan, combine 3 cups of sliced rhubarb with 1/2 cup of granulated sugar, 2 tablespoons of lemon juice, and 2 teaspoons of cornstarch. Cook for about 10 minutes until thickened.

Roll Out Dough: Once risen, punch down the dough and roll it into an 18x12-inch rectangle. Spread the cooled rhubarb filling evenly over the dough, leaving a 1-inch border.

Shape Rolls: Starting from the long edge, roll the dough tightly into a cylinder. Cut the roll into 12 equal pieces and place them cut-side up in a greased 9x13-inch pan. Cover and let rise until puffy.

Preheat Oven: Preheat the oven to 350°F (175°C). Ensure the oven is fully preheated when the rolls finish their second rise.

Egg Wash: Whisk together 1 beaten egg and 1 tablespoon of water or milk to create an egg wash. Brush the tops of the rolls before baking.

Bake: Bake the rolls for 25-30 minutes until golden brown and the dough sounds hollow when tapped.

Prepare Glaze: Mix 2 tablespoons of the rhubarb filling with 1 cup of powdered sugar and 1-2 tablespoons of lemon juice until smooth.

Glaze Rolls: Let the rolls cool for about 10 minutes, then pour the pink glaze over the warm rolls.