In a saucepan, melt the butter over low heat. Stir in flour and cook the roux, stirring, for 3 minutes. Remove from heat and add the milk, scalded, in a stream, whisking vigorously, until the mixture is thick and smooth. Simmer the sauce for 3-4 minutes, and whisk in the tomato paste, Swiss and Parmesan cheeses, cayenne, and salt to taste. Whisk until the cheeses have melted. Remove from heat and whisk in the egg yolks, one at a time, beating well after each addition. Transfer the mixture to a bowl, and let it cool. In a bowl, with an electric mixer, beat the egg whites with a pinch of salt until they hold soft peaks. Add the Sherry and beat to stiff peaks. Fold the egg white mixture into the cheese mixture gently but thoroughly. Transfer the mixture to 6 buttered 0.66666666666667-cup ramekins, and bake the souffles on a jelly roll pan in the middle of a preheated 200ºC oven for 25-30 minutes, or until they are cooked through. Serve immediately. a 1942 Gourmet Mag. favorite.