Preheat your oven to 200°C (400°F) and grease six ramekins with butter or cooking spray.

In a large skillet, melt 2 tablespoons of unsalted butter with 1 tablespoon of olive oil over medium heat. Add finely chopped shallots and sauté for about 3-4 minutes until translucent.

Add 3 cloves of minced garlic and 500 grams of mixed mushrooms. Cook for 6-8 minutes until mushrooms release moisture. Season with fresh thyme, salt, and black pepper.

Sprinkle 2 tablespoons of flour over mushroom mixture, stir for 1 minute. Pour in 120 ml of white wine, reduce until nearly evaporated.

Slowly add 240 ml of whole milk while stirring. Cook for an additional 2-3 minutes until thickened. Add 100 grams of Gruyère and 1 teaspoon of Dijon mustard.

Remove from heat and let filling cool for 10-15 minutes.

Roll out puff pastry on a floured surface and cut out circles larger than the ramekins.

Spoon filling into ramekins, cover with pastry, crimp edges, and make a small slit for steam to escape.

Brush pastry with beaten egg and sprinkle thyme leaves.

Bake in preheated oven for 18-22 minutes until golden brown and puffed.