Fold beaten egg whites into egg yolk/mascarpone mix. IMPORTANT: Add egg whites a few tablespoons at a time and perform a folding move from the bottom of the bowl curling over the top. Do this as gently as possible in order not to crush light and airy texture of the beaten egg whites.
NOTE: you might not use ALL of the egg whites. Stop when you feel you've reached the desired consistency of the cream. It should not be too liquid.