6 egg yolks, beaten
2 cups whipping cream
1 teaspoon chopped, fresh rosemary
Salt and freshly cracked black pepper, to taste
Pinch red-pepper flakes
4 medium celeriacs (celery roots), peeled
2 medium russet potatoes, peeled
Olive-oil spray, as needed
1/2 bunch green onions, chopped (green tops only)
6 ounces aged Gouda, grated

Preheat oven to 325 F.

In a large stainless-steel bowl, beat together the egg yolks, whipping cream, rosemary, salt, pepper and pepper flakes.

Thinly slice the celery root and potatoes; place in egg mixture. Coat an 8-by-12-inch casserole dish with olive-oil spray.

Stir mixture to coat celery root and potato. Lay down 1 layer of celery root and potato slices in dish. Top with some of the green onion and Gouda. Continue layering until all ingredients are used. Pour remaining custard over vegetables to cover.

Bake in preheated oven, uncovered, for 1 hour. Pierce with a knife; there should be no resistance from vegetables or raw custard visible. Let rest briefly.

Makes 6 servings.

— Recipe from Roots Restaurant and Cellar in Milwaukee, Wis.