Preheat oven to 400°F. Place a rack in the lower third of the oven.

Butter and flour a 7-inch soufflé dish or another deep baking dish with straight sides. Set aside.

Melt butter in a saucepan over low heat. When melted, add flour and stir in. Add bay leaf and grated nutmeg. Continue stirring and cooking for 4 to 5 minutes, until golden brown.

Slowly add milk to flour mixture, stirring all the time. Increase heat to medium, cook until thickened and just starting to boil, stirring continuously, about 10 minutes. Remove from heat. Remove bay leaf.

In a large bowl, blend egg yolks and cheese. While stirring rapidly, slowly add hot cream sauce until completely mixed in.

Combine egg whites and cream of tartar in the mixing bowl of a stand mixer, and whip until it holds stiff, but not dry, peaks.

In three additions, fold the whipped egg whites into the cheese mixture.

Scrape into prepared pan and bake until puffed, golden brown, and a skewer inserted into the center comes out clean, about 30 minutes. Serve immediately.