Root Vegetable Gratin

Slice all vegetables on a mandoline to a thickness of 2 mm.

In a large pot, bring water to a boil and add salt. Blanch sweet potatoes and celery for 30 seconds. Then transfer them to ice water to stop the cooking.

Blanch the potatoes for a minute and then send them to ice water.

For béchamel sauce, melt butter in a saucepan. Add flour and sauté, stirring, until golden brown.

Add warm milk and cream, bring to a boil while constantly stirring with a whisk.

Add thyme leaves and parmesan. Stir until it reaches a sour cream consistency.

Line the baking dish with parchment paper.

Spread a little sauce in a thin layer at the bottom.

Layer the sweet potato slices so the bottom is not visible. Salt and brush with a small amount of béchamel.

Next, layer the potatoes. Salt them and brush with sauce. Then layer the celery in the same way, salt it and brush with sauce. Continue layering all the vegetables in the dish.

Spread the last layer with béchamel and send the gratin to the oven preheated to 180 degrees for 45–50 minutes.

Check the gratin for doneness by poking it with a skewer, cover with a press, and leave it until completely cool.

Remove the cooled gratin from the mold by flipping it over and cut into portion pieces. Reheat in the oven and serve.