Czech Koláče with Sweet Poppy Seed Filling and Streusel Topping

In a small bowl, combine 1/2 cup warm milk, 1 teaspoon sugar, and 2 1/4 teaspoons active dry yeast. Let stand for 5-10 minutes until foamy.

In a large bowl, whisk together 2 1/2 cups all-purpose flour, 1/4 cup granulated sugar, and 1/2 teaspoon salt. Add the foamy yeast mixture, 1 large egg, and 1/4 cup melted butter. Mix until a shaggy dough forms, then knead on a lightly floured surface for 5-7 minutes until smooth and elastic. Place the dough in a lightly oiled bowl, cover, and let rise in a warm place for 1 hour, or until doubled in size.

While the dough rises, prepare the poppy seed filling: In a small saucepan, combine 1 cup ground poppy seeds, 1/2 cup whole milk, and 1/4 cup granulated sugar. Bring to a simmer over medium heat, stirring constantly, until thickened (about 5 minutes). Remove from heat and stir in 1/2 teaspoon vanilla extract. Let cool completely.

Prepare the streusel topping: In a small bowl, combine 1/2 cup all-purpose flour, 1/4 cup granulated sugar, and 1/4 cup cold unsalted butter. Use your fingertips to rub the butter into the dry ingredients until coarse crumbs form.

Once the dough has risen, punch it down gently. Divide the dough into 12 equal pieces. Roll each piece into a ball and place them 2 inches apart on a baking sheet lined with parchment paper. Using the bottom of a glass or your thumb, create a deep indentation in the center of each dough ball. Fill each indentation with about 1 tablespoon of the cooled poppy seed filling.

Sprinkle the streusel topping generously over the filled koláče. Let them rise again for 20 minutes.

Bake the koláče in a preheated oven at 375°F (190°C) for 20-25 minutes, or until golden brown and cooked through. Let cool on a wire rack before serving.