Begin by peeling and dicing your Yukon Gold potatoes into small cubes. Boil them in a pot of salted water for about 15–20 minutes, or until they are fork-tender. After draining the potatoes, allow them to cool for a few minutes so they are easier to handle.

In a large skillet, melt 2 tablespoons of butter over medium heat. Add the chopped yellow onions and sauté them for about 5–7 minutes until tender and translucent. Transfer the sautéed onions to a bowl to cool slightly.

In a large mixing bowl, combine the cooled potatoes and sautéed onions. Grate in sharp cheddar cheese, add 1/4 cup of heavy cream, 1 tablespoon of Dijon mustard, and a tablespoon of all-purpose flour. Season with kosher salt and black pepper to taste, and mix thoroughly until combined.

On a lightly floured surface, roll out your chilled frozen puff pastry until it's about 1/8 inch thick. Cut the dough into rectangles, approximately 5x4 inches. Spoon a generous amount of the creamy filling onto one half of each pastry piece.

To seal the hand pies, fold the pastry over the filling and press the edges together. Use a fork to crimp the edges or your fingers to pinch them closed securely. Brush an egg wash over the tops.

Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper. Bake the hand pies for 25–30 minutes, or until they are puffed and golden brown. Allow them to cool slightly before serving.

Enjoy your Cheese Onion and Potato Hand Pies warm as a delightful snack or appetizer.