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

Melt 2 tablespoons of unsalted butter and 1 tablespoon of olive oil in a skillet over medium heat. Add the chopped shallot and sauté for 2-3 minutes until translucent. Add 2 cloves of minced garlic and cook for an additional minute.

Add 500 grams of mixed mushrooms and cook for 5-7 minutes until tender. Season with fresh thyme leaves, salt, and black pepper.

Sprinkle 2 tablespoons of all-purpose flour over the mixture and stir for about 1 minute. Gradually pour in 100 ml of dry white wine, stirring until nearly evaporated.

Pour in 250 ml of whole milk slowly, mixing until thickened. Add 150 grams of grated Gruyère cheese and 1 teaspoon of Dijon mustard, stirring until melted and creamy.

Cool the filling slightly for about 5 minutes.

Unroll a sheet of thawed puff pastry and cut out circles 1-2 inches larger than the ramekins.

Spoon filling into the ramekins and top with pastry, sealing edges. Cut a small slit in the center for steam to escape.

Whisk together an egg and a splash of water for the wash. Brush over the pastry and sprinkle with extra thyme leaves.

Bake in the preheated oven for 18-22 minutes or until golden brown.

Allow to cool for about 5 minutes before serving, garnished with extra thyme.