Once toasted, place the toasted walnuts and garlic cloves, basil leaves, cheese, and lemon juice in the bowl of a food processor. Pulse the pesto for about 30-40 seconds, until everything is thoroughly combined and the basil leaves are finely chopped. With the food processor running (I use the high speed setting), drizzle the olive oil through the feed chute until you reach the desired consistency, add more or less olive oil as needed. I use about 2/3 cup + 2 tablespoons of olive oil for my pesto, but the final amount usually varies each time by a couple of tablespoons. If you'd like thicker pesto, use less olive oil. Finally, stir in the salt and pepper. I use 1/2 teaspoon of salt, but this amount will vary according to your taste, which is why it's added at the end.