Preheat oven to moderate (325°F.) and place the rack near the bottom of the oven. Grease a jelly-roll pan (10 × 15 inches); line pan with wax paper greased and sprinkled with flour.
Melt the butter, blend in the flour with a wire whisk, add the milk, and cook, stirring, until mixture boils. Simmer, stirring, for one minute.
Add a little hot sauce to the beaten egg yolks, then blend yolks with the hot sauce. Beat egg whites until stiff and fold into the mixture.
Spread the batter in the prepared pan and bake for about forty minutes. Meanwhile, prepare filling. Remove cake when it rebounds to the touch and top is a deep golden brown. Turn out on wax paper.
While roll is baking, mix the cream cheese and three tablespoons of the sour cream. Add half of the caviar and mix gently. Spread lightly on turned-out cake. Roll the cake like a jelly roll.
Make a sauce by blending remaining sour cream and caviar. Additional caviar may be added to the sauce if desired, and additional caviar also may be stirred into the filling before it is spread on the cake.
Cut the cake into thin slices and top each slice with a spoonful of the sauce.