If you can't obtain authentic Mexican crema, don't fret as you can make it at home. If you can't be bothered doing that, I suppose you can always substitute it with regular sour cream, but don't be upset if I decline your next dinner invitation.
Makes 1 cup crema
1
cup heavy whipping cream2
tsp buttermilk
Mix the heavy whipping cream and buttermilk. The cream should be at room temperature. Let it culture for one day in a warm place until thickened. Presto! Your cream has now soured and you have Mexican crema. Refrigerate and use within two weeks.