The ripe avocado can be recognized by the fact that it gives way very easily when pressed lightly.
You cut it in half once, cut off one side and quarter it. Take out the core. Scoop out the avocado with a spoon and place the pulp in a tall bowl. Add lemon juice, pepper, salt and quark and puree everything until creamy. Try once, the lemon should be easy to taste. If not, just give in a little and stir vigorously with a spoon again.