Try our easy, mini version of Beef Wellington. Mushrooms, onion and thyme paired with Beef Tenderloin and baked in pastry cups until golden and crisp. These bite-sized appetizers quickly come together and are perfect for entertaining.
In large nonstick skillet, heat 1 tablespoon oil over medium-high heat. Add mushrooms; cook 2 to 3 minutes until tender and all liquid is evaporated, stirring often. Stir in onion, thyme, 1/4 teaspoon salt and 1/4 teaspoon pepper; remove from heat and set aside.
Preheat oven to 425°F. Toss beef with remaining 1 tablespoon oil, 1/2 teaspoon salt and 1/4 teaspoon pepper.
Spray 24 mini-muffin cups with cooking spray. Unfold puff pastry on a lightly floured cutting board; cut each sheet into 12 (2-inch) squares. Place squares into mini-muffin cups. Brush dough with mustard, then place heaping teaspoon of mushroom mixture in center of dough. Top with steak piece.
Bake 10 to 12 minutes or until golden brown and instant-read thermometer inserted in center registers 135°F for medium rare; 150°F for medium. Let rest. Temperature will continue to rise to 145°F for medium rare and 160°F for medium.
Serve warm topped with horseradish sauce and parsley, if desired.