Wipe the mushrooms clean with a damp towel and tear them into 2 cm pieces. Dice the shallots, mince the garlic, strip the thyme leaves, and grate the Gruyère.

Blend the flour, eggs, milk, melted butter, and 1/4 tsp salt for 20 seconds until smooth, scraping down the sides once. Pour into a jug, cover, and refrigerate for 30 minutes.

Heat a 20 cm / 8-inch nonstick skillet over medium heat and rub it lightly with a little of the 2 tsp butter. Stir the rested batter, which should pour like heavy cream, then pour in 60 ml / 1/4 cup and tilt the pan so it coats the base.

Cook for about 1 minute until the edges lift and the surface looks matte, then flip and cook 20 seconds more. Slide onto a plate and repeat to make 8 crepes, re-buttering the pan only when the crepes start to stick. This takes about 12 minutes.

Heat 1 tbsp of the olive oil in a 30 cm / 12-inch skillet over medium-high heat until it shimmers. Add half the mushrooms in a single layer and leave them alone for 2 minutes, then stir and cook 3 to 4 minutes more until browned and the pan looks dry. Move to a bowl and repeat with the remaining oil and mushrooms.

Lower the heat to medium and melt the 1 tbsp butter in the same skillet. Cook the shallots for 2 minutes until soft, add the garlic and thyme for 30 seconds, then pour in the wine and simmer 1 minute until nearly gone. Return the mushrooms with 1/2 tsp salt and the pepper.

Add the spinach by the handful, stirring until wilted, about 2 minutes. Stir in the crème fraîche, nutmeg, and lemon juice and simmer 1 to 2 minutes until the sauce is thick enough to hold on a spoon. Taste and add salt if needed.

Heat the oven to 190 C / 375 F with a rack in the center and butter a 23 x 33 cm / 9 x 13-inch baking dish. Spoon about 3 tbsp of filling down the center of each crepe, roll it up, and place it seam-side down in the dish.

Sprinkle the Gruyère over the crepes and bake for 10 minutes until the cheese is bubbling and the crepe edges are lightly crisp. Scatter with parsley and serve hot.