Belarusian Pirog Recipe - Traditional Savory Pie

Ingredients

• 2 cups all-purpose flour
• 1/2 cup unsalted butter, cold and cubed
• 1/2 cup sour cream
• 1 large egg
• 1/2 teaspoon fine sea salt
• 1 teaspoon granulated sugar
• 1/2 teaspoon baking powder
• 1/2 pound cremini mushrooms, finely chopped
• 1 medium yellow onion, finely diced
• 2 tablespoons unsalted butter (for filling)
• 1/2 pound Yukon Gold potatoes, peeled and diced
• 1/4 cup heavy cream
• 1/4 cup fresh dill, finely chopped
• 1/2 teaspoon freshly ground black pepper
• 1/2 teaspoon kosher salt (for filling)
• 1 egg yolk (for egg wash)
• 1 tablespoon milk (for egg wash)