1. Preheat your oven to 400°F and grease a mini muffin pan.

2. In a skillet, heat the olive oil over medium-high heat. Add the diced onion and sauté for about 3 minutes, until softened.

3. Toss in the diced cremini mushrooms, salt, pepper, and dried thyme (if using). Cook the mushroom mixture, stirring occasionally, until the mushrooms release their liquid and it evaporates, about 8 to 10 minutes. Stir in the minced garlic and cook for 30 seconds. Allow the filling to cool for 5 minutes before mixing in the shredded cheese.

4. Unfold the thawed puff pastry sheets and lightly roll them out to even out any creases. Cut each sheet into 9 squares, resulting in 18 pastry squares in total.

5. Press one puff pastry square into each mini muffin cup, gently shaping it to form a little “cup.” Spoon about 1 to 1 1/2 tablespoon of the mushroom-cheese filling into each pastry cup. Finish by brushing the exposed pastry edges with the beaten egg.

6. Pop the filled Mushroom Cheese Puff Bites into the preheated oven and bake for 15 to 18 minutes, or until the pastry is puffed and golden brown.