3 tablespoons unsalted butter (plus extra for buttering the dish)
1/4 cup Parmesan cheese (finely grated)
3 tablespoons unbleached all-purpose flour
1 pinch cayenne pepper
1 pinch freshly ground nutmeg
1 cup whole milk
4 large egg yolks
1 1/2 cups cooked broccoli (chopped, no pieces larger than 1/3 inch)
5 large egg whites