Cook and cool the baby potatoes.

Start the baby potatoes in well-salted cold water, testing them with a knife blade so they do not overcook; they cook for about 15 minutes.

Slice the onions and make an onion confit.

In a skillet over medium heat, warm a generous drizzle of olive oil and add a large knob of butter.

When the butter foams, add the onions and salt them.

Keep the onions over medium heat, then lower to low once heated and cook for about 40 minutes, half-covered, stirring occasionally.

Heat the oven to 200 degrees.

Slice the mushrooms and sauté them in a very hot skillet with a drizzle of olive oil.

When the mushrooms have released their water, lower the heat, salt them, and set aside.

Whisk the eggs in a mixing bowl, add the heavy cream, chives, black pepper, salt, and Parmesan, then mix.

Brush the pastry ring with butter.

Crush the baby potatoes in the base using a glass; do not overlap them.

Crush the edge potatoes between your hands and arrange them around the edge.

Add the onions, mushrooms, and egg-cream mixture, then mix well.

Lower the oven to 180 degrees just before baking for about 45 minutes or until golden.

Serve with green salad, vinaigrette, and more fresh chives on top.