1. Make the cocktail sauce by first making a mayonnaise.
All ingredients should be at room temperature. In a bowl, mix the egg yolk, a pinch of salt, a pinch of pepper, mustard, and vinegar or lemon juice. Whisk continuously while slowly pouring in the oil. The mayonnaise should gradually thicken.
2. For the cocktail sauce, mix all the ingredients together and the cocktail sauce is ready!
3. Wash and dry the basil leaves.
4. Cut the avocados in half and remove the pit. Peel the avocados and cut them into small slices.
5. In 4 individual bowls, gently mix the avocado slices, shrimp, and cocktail sauce.
6. Garnish with a few fresh basil leaves.