In a small, heavy saucepan, melt butter over low heat. Add flour and cook, whisking constantly, about two minutes, until foaming but not browned. Remove from heat. Gradually whisk in the milk, bring to a boil over medium-high heat, whisking, reduce heat to low, continue to cook, still whisking, about two minutes. Whisk in spinach puree and goat cheese, bring to a simmer. Season lightly with salt, pepper and nutmeg.
05Remove from heat and whisk in the egg yolks, one at a time. Heat gently until slightly thickened, but do not allow to boil. Re-season if necessary.06Beat egg whites with cream of tartar until stiff but still supple. Quickly fold one-quarter of the whites into the warm spinach mixture. Spoon the mixture into the remaining whites and fold in lightly but quickly.07Transfer mixture to prepared souffle dish and smooth the top. Bake 20 minutes till puffed and browned. Souffle should shake slightly in the center when the dish is moved. Do not overbake. Serve at once.