Preheat your oven to 400°F (200°C) and prepare six 6-ounce ramekins by greasing them with butter or cooking spray.

Unroll puff pastry on a floured surface, and cut out circles larger than your ramekins.

Melt unsalted butter in a skillet over medium heat, add chopped onions, and sauté for about 4 minutes until translucent.

Add chopped mixed mushrooms and minced garlic to skillet, cooking for 8-10 minutes until mushrooms are golden brown.

Sprinkle in thyme and flour, mixing for 2 minutes to eliminate raw flour taste.

Gradually pour in vegetable broth, stir to avoid lumps, and bring to a gentle simmer.

Mix in heavy cream after thickening, and cook for an additional 5 minutes.

Season filling with salt and black pepper to taste.

Divide the mushroom mixture among ramekins and sprinkle Gruyère cheese on top.

Cover filled ramekins with puff pastry, sealing the edges well.

Brush the puff pastry with beaten egg for a golden color.

Bake pot pies for 15-20 minutes until pastry is golden and puffy.

Let pot pies cool for 10 minutes before serving.