Pick the leaves from the stems and measure the required amount.
Place about half of the leaves in a food processor; they will probably fill the processor. Process them shortly to make space for the remaining ingredients.
Add the remaining leaves, nuts, chopped cheese, oil, lemon juice, salt, and pepper.
Process until smooth, scraping the walls of the food processor a few times in between.
Adjust the taste with more salt, pepper, and lemon juice (if necessary).
Transfer to jars.
Notes
Only measure the lovage after removing the leaves from the stems. You will need more or less 2 large bunches.
I use sunflower or canola oil or a mixture of them. Olive oil is also fine, preferably a lighter sort.
Parmesan is not vegetarian; for a vegetarian pesto, use vegetarian hard cheese. Please use freshly grated cheese, not pre-grated.
To give the pesto a bit of heat, add some cayenne pepper. I add about 1/8 teaspoon, but please use to taste.