In a food processor with the blade running, drop the garlic through the feed tube to chop. Add the herbs (whatever you have—feel free to use a mix!) and nuts or seeds. Process until finely chopped.
Add a splash of lemon juice, lime juice or red wine vinegar. I usually squeeze in the juice of a ½ small lemon or lime, or start with about 1 teaspoon of red wine vinegar (remember, you can always add more but you can’t take it out!). Season with salt and pepper. If using any add-ins, add them now and puree until finely chopped.
If you prefer a lighter sauce, add a tablespoon or two of water. With the motor running, drizzle in extra virgin olive oil until you get a spoonable, pesto-ish consistency.
This is the most important step: taste the sauce! This is your time to adjust the seasonings as desired. More nuts will thicken up the sauce, a splash more acid will give the sauce more spunk, and another drizzle of olive oil will round things out. There should be a good balance of flavors, and the final result should taste good to you. If you have the time, let the sauce sit, covered, for 15 minutes to allow the flavors to meld before serving.