Preheat the oven to 400?F.
Heat a large skillet over high heat. Add the beef and cook, stirring, until well browned, about 5 minutes. Add the onions, garlic, Essence, crushed red pepper, and 1/4 teaspoon salt and cook, stirring, until the onions are soft and lightly caramelized, about 7 minutes. Add the tomato paste and heavy cream and cook until the cream is evaporated, 1 to 2 minutes. Remove from the heat and spread on a plate to cool.
In a large skillet, melt the butter over medium-high heat. Add the mushrooms, thyme, Worcestershire, and the remaining 1/4 teaspoon salt and cook, stirring often, until most of the liquid has evaporated, 8 to 10 minutes. Remove from the heat and spread on a plate to cool.
Combine the egg and water in a small bowl to make an egg wash. Whisk to combine.
On a lightly floured surface, roll out the puff pastry sheets, 1 at a time, to a 1/8-inch thickness about 11 inches square. Brush 1 short edge of 1 sheet with egg wash and overlap with the other. With the rolling pin, press down on the seam to make 1 large sheet. Spread the cooled Mashed Potatoes along the lower third of the pastry, leaving a 1-inch border on 3 sides. Top with the beef and the mushrooms, then sprinkle the Gouda cubes over the top. Brush the border with egg wash and fold the pastry over the filling to completely enclose. Press to seal the edges tightly with the tines of a fork. Transfer to a large baking sheet and brush with the egg wash. Cut 5 small steam vents in the top of the pastry. Bake until starting to turn golden brown, 15 to 16 minutes. Sprinkle the top with the Cheddar and bake until the pastry is golden brown and the cheese is melted, about 4 minutes.
Remove from the oven and let rest for 5 minutes. Transfer to a large serving platter. Slice and serve warm.
Makes 6 servings