Prepare the Dough: In a stand mixer, combine the warm whole milk, dry active yeast, granulated sugar, pure vanilla extract, melted Kerrygold salted butter, and large egg. Allow the mixture to rest for 5 minutes until frothy.

Knead the Dough: Add unbleached all-purpose flour and kosher salt to the yeast mixture. Using a dough hook, knead the dough on medium speed for about 12–15 minutes until smooth and elastic.

First Rise: Transfer the dough to a lightly oiled bowl, cover with a damp cloth or plastic wrap, and let it rise for approximately 1 hour until doubled in size.

Make the Cream Filling: In a mixing bowl, combine cream cheese, full-fat sour cream, vanilla extract, powdered sugar, and lemon zest until smooth and creamy.

Shape the Buns: Punch down the risen dough, turn it out onto a floured surface, and divide into 12–15 equal pieces. Roll each piece into a ball and place on a parchment-lined baking sheet.

Fill the Buns: Create an indentation in each dough ball, pipe in the cream filling, add blueberry preserves, and top with fresh blueberries.

Egg Wash and Bake: Beat an egg and brush it around the edges of each filled bun. Bake in a preheated oven at 350°F for approximately 25 minutes until golden brown.

Garnish and Serve: Let the buns cool on a wire rack before sprinkling with powdered sugar. Serve warm.