Prepare Yeast Mixture: Warm the milk until just warm (about 30 seconds in microwave). In a small bowl, mix 1 teaspoon active dry yeast with 1 tablespoon granulated sugar and the warm milk. Let it sit for about 10 minutes until foamy.
Mix Dough Ingredients: In a mixing bowl, combine 1 tablespoon granulated sugar, 1 3/4 cups all-purpose flour, and 1 large egg. Add the foamy yeast mixture and mix with a hook attachment until the flour absorbs most of the milk.
Add Butter and Knead: Add half a stick (about 4 tablespoons) of softened unsalted butter to the dough. Knead with the hook attachment for 8 minutes until the dough is soft, fluffy, and not sticky.
First Rise: Sprinkle a little flour on top of the dough, cover the bowl with a clean kitchen towel, and let it rise in a warm place for 1 hour until doubled in size.
Prepare Blueberries: Wash the blueberries and dry them thoroughly on paper towels to remove excess moisture.
Make Crumble Topping: In a bowl, combine 1/3 cup all-purpose flour, 2 tablespoons powdered sugar, and 2 tablespoons softened unsalted butter. Mix with fingers until crumbly with no large butter chunks. Set aside.
Make Sugar Glaze: Whisk together 1/3 cup powdered sugar and 2 tablespoons water until smooth. Set aside for glazing after baking.
Shape Kolaches: Turn the risen dough onto a floured surface. Divide into 8 equal portions (use a scale for accuracy if desired). Shape each portion into a ball and place on a baking tray lined with parchment paper, spacing them evenly.
Second Rest: Let the shaped dough balls rest for 5 minutes while preheating the oven to 380°F (193°C).
Press Centers: Lightly flour a wooden kolache press or similar tool. Press the center of each dough ball to create a well for the blueberries.
Brush with Butter: Brush the sides of each kolache with 1/2 tablespoon melted unsalted butter, avoiding the center.
Fill and Top: Fill the center wells with blueberries. Generously sprinkle the crumble topping over each kolache.
Bake: Bake in the preheated oven at 380°F (193°C) for 16-17 minutes or until golden brown.
Glaze and Cool: Immediately after baking, brush the kolaches with the prepared sugar glaze. Transfer to a cooling rack and let cool before serving.
Storage: Once cooled, kolaches can be frozen in zip-lock bags for later use. Reheat briefly in microwave or toaster oven before serving.