Grease jelly roll pan, 15 ½ x 10 ½ inch. Line bottom of pan with waxed paper; grease lightly and flour. Heat butter over medium heat until melted. Remove from heat; stir in flour.
Cook over low heat, stirring constantly, until smooth and bubbly. Remove from heat; stir in milk. Heat to boiling, stirring constantly. Boil and stir 1 minute. Remove from heat.
Blend in cheddar and lightly beaten egg yolks, one at a time. Beat egg whites and cream of tartar in large mixer bowl until stiff but not dry. Stir about ¼ of the egg whites into egg yolk
mixture. Gently fold egg yolk mixture into remaining egg whites. Pour into pan. Bake at 350 until puffed and golden brown, about 15 - 20 minutes
While soufflé roll is baking, sauté onion and almonds in 2 tbsp. butter. Sprinkle with 1 tbsp. flour; stir to blend. Add
seasonings and asparagus. Stir for 5 minutes, or until most moisture evaporates. Remove from heat.
With metal spatula, loosen edges of soufflé; turn out on tea towel; (See Warning) spread
asparagus mixture gently on top; sprinkle with Swiss cheese. Roll up jelly roll fashion; place on serving dish. Let stand a few minutes in warm oven. Mix sour cream and mustard
together, serve over soufflé roll.