If you love roast beef, you will adore these beef-filled flaky packets of puff pastry. Roast Beef Wellington Packets really satisfy the hard-working appetites at my house!
Preheat the oven to 375 degrees F.
In a large saute pan or skillet over medium high heat, melt the butter. When the butter is sizzling a bit, add the mushrooms and garlic, cooking for 2-3 minutes or until the mushrooms are softened slightly and the garlic is fragrant; remove from heat and let the mushroom mixture cool slightly.
Meanwhile, in a large mixing bowl, gently toss the chopped roast beef and cheese together, then add the mushrooms and garlic mixture and toss once more.
Unwrap the puff pastry and lay one sheet out onto a very lightly floured work surface. Using a rolling pin, roll out the puff pastry to about 12" x 12" in size, then cut in half diagonally to create two triangles.
Place one quarter of the prepared roast beef filling onto one side of the puff pastry triangle, leaving about 1/2" of space around the outer edge of the triangle; fold the dough over the filling. Using a fork, press the edges of the dough together to seal tightly; brush the pastry with egg wash. Repeat with the remaining puff pastry dough and filling.
Bake the roast beef packets, uncovered, on the center rack of the preheated oven for 20-25 minutes, or until nicely golden brown, puffy and hot throughout.
Serve warm, with the prepared horseradish sauce on the side for dipping.