To make the Sweet Watruschka Dough
1-Begin by making the Sweet Watruschka Dough: Begin by making the Sweet Watruschka Dough. In a small bowl, combine the yeast and warm water, stirring gently. Let this sit for about 8 to 10 minutes to allow the yeast to activate. It should begin to bubble and grow if it is active.
2-In a small saucepan, combine the milk,: In a small saucepan, combine the milk, sugar, and salt. Place it over medium-low heat, and warm the milk until it begins to steam, or reaches 110° F (43° C). Pour the warmed milk mixture into the bowl of an electric standing mixer fitted with a dough hook attachment along with the yeast mixture. Whisk to combine, then add the egg yolks.
3-Begin to slowly incorporate the flour, about: Begin to slowly incorporate the flour, about 1 cup (125 g) at a time until the dough begins to form and no longer clings to the sides of the bowl. Then, add the softened butter and knead it into the dough for about 10 to 12 minutes on medium-high speed or until the dough becomes soft, elastic, and pillowy. Alternately, you can make this dough by hand or in a bread machine up until the first rise.
4-Once the dough is soft, smooth, and: Once the dough is soft, smooth, and elastic bring it out onto the countertop and shape it into a tight ball. Lightly grease a large bowl and place the dough in the bowl. Cover the bowl with a warm, damp towel or plastic wrap and allow it to rise until doubled in size, about 1 hour.

To make the Blueberry Sauce
5-While the dough is rising, make the: While the dough is rising, make the Blueberry Sauce. In a small saucepan, combine the blueberries, sugar, lemon juice, and water. Place the saucepan over medium heat and bring the mixture to a boil.
6-Lower the heat to a simmer and: Lower the heat to a simmer and continue to cook the sauce for about 8 to 10 minutes or until slightly thickened. Remove the saucepan from the heat and let the mixture cool while you continue with the rest of the recipe.
7-To prevent a skin from forming over: To prevent a skin from forming over the top of the sauce, you can place a piece of plastic wrap over it, touching the surface of the sauce.

Shaping the Buns
8-Now that the dough has finished rising,: Now that the dough has finished rising, gently deflate it with your hands. Divide the dough into 12 equal sized pieces.. Form the dough into balls, pinching the seam closed. Lightly grease 2 large baking sheets and arrange the buns on the sheets about 4-inches (10-cm) apart. Cover the buns with plastic wrap and let them rise for about 20 to 30 minutes. They will not be fully puffed like other bread recipes.

To make the Ricotta Cheese Filling
9-Meanwhile, make the Ricotta Cheese Filling: Meanwhile, make the Ricotta Cheese Filling. In a medium bowl, whisk together the ricotta or quark, eggs, sugar, vanilla, cornstarch, and heavy cream until smooth and there are no large lumps. You will want the sugar to be almost completely dissolved in the cheese, so an electric mixer would be the best option to mix this quickly!

To Bake the Buns
10-Preheat your oven to 350° F (180°: Preheat your oven to 350° F (180° C)
11-With the bottom of a drinking glass: With the bottom of a drinking glass or small canning jar, press firmly down on the center of each bun to make a well that is deep and wide enough to hold 2 tablespoons (30 ml) of filling. Be careful not to press too much and make a hole in the dough. It helps to spray the bottom of your glass with a light layer of cooking spray or oil so that it does not stick to the buns. It should look like a little nest with a flat bottom and rounded sides, and you can use your finger to press the indentation down more evenly.
12-Place 1 tablespoon (15 ml) of the: Place 1 tablespoon (15 ml) of the Cheese Filling into the wells of each bun. Then, place 1 tablespoon (15 ml) of the Blueberry Sauce into the wells of each bun.
13-In a small bowl, whisk together the: In a small bowl, whisk together the remaining egg and heavy cream for the egg wash. Brush this all along the sides of each bun. Bake the buns for about 20 minutes or until golden brown in the preheated oven. Serve the buns warm or at room temperature.