In a large frying pan, sauté the mushrooms in a splash of olive oil/butter until golden brown.
Add the garlic and thyme and sauté for another minute before stirring in the flour.
pour in the vegetable stock and cream and whisk until the sauce is smooth. Allow to simmer gently for 5-10 minutes then season with the lemon juice, salt and pepper.
Transfer the creamy mushrooms to individual oven-proof ramekins/bowls.
Roll the pastry out on a floured surface and cut out circles big enough to fit the ramekins.
Press the pastry onto the sides of the ramekins and crimp the sides. Cut a small slit into the pastry to allow steam to escape then brush with the egg yolk.
Place in the oven and allow to bake for 15-20 minutes until the pastry is golden brown and cooked through.