Mini Tarts with Roast Beef and Gruyère

Name: Mini Tarts with Roast Beef and Gruyère
Prep time: 30 min
Cook time: 20 min
Total time: 50 min
Cuisine: European, Mediterranean, French
Ingredients: frozen prepared mini tart shells; g thinly sliced roast beef; tablespoon butter; shallot, finely diced; cup mushrooms, thinly sliced; tablespoon fresh thyme, chopped; tablespoon prepared horseradish; cup cream cheese; egg, room temperature; cup Gruyère cheese, grated; salt and pepper