In a mixing bowl, combine 4 cups of all-purpose flour, 2 teaspoons of active dry yeast, and 1 teaspoon of salt. Warm 1 cup of whole milk to about 110°F, then stir in 1/4 cup of granulated sugar, allowing it to dissolve. Add this mixture to the flour along with 3 room-temperature eggs and 1/2 cup of softened unsalted butter. Mix until the dough forms a ball and knead for 5-7 minutes until smooth and elastic.

Transfer the kneaded dough to a greased bowl, covering it with a damp cloth or plastic wrap. Place it in a warm spot, allowing it to rise until it doubles in size, about 1 to 1.5 hours.

In a saucepan, combine 2 cups of diced fresh rhubarb, 1 cup of granulated sugar, and 1 tablespoon of lemon juice. Cook over medium heat, stirring occasionally until the mixture thickens, approximately 10-15 minutes.

Once the dough has risen, punch it down to release excess air, then turn it out onto a floured surface. Roll the dough into a large rectangle, about 1/4 inch thick.

Evenly spread the cooled rhubarb quick jam over the rolled-out dough, then roll the dough into a tight log, pinching the seam to seal it. Slice the log into 12 equal pieces.

Place the cut pieces into a greased 9x13-inch baking dish, cover with a damp cloth, and let them proof for another 30-45 minutes.

Preheat your oven to 375°F. Bake the sticky buns for 25-30 minutes or until the tops are golden brown.

In a mixing bowl, blend together 8 ounces of mascarpone cheese, 1/2 cup of powdered sugar, 1 tablespoon of vanilla bean paste, and 1/4 cup of heavy whipping cream until smooth and creamy.

Once the buns have cooled for about 10 minutes, generously spread the frosting over each sticky bun.