When harvesting basil, look for the two largest leaves on a stem, just below those you should see another set of leaves or little knobs (nodes) that are growing in between the stem smaller set of leaves. Cut the stem 1/4-1/2″ above the nodes. Repeat this with all the larger leaves on your plants. See Figure 1, Harvesting Basil.
Harvesting frequently will help prolong the life of the plant. The best taste is just before the plant flowers, and to delay flowering, pinch or clip off new flower buds. See Figure 2, flower buds.
Whenever you want a fresh garnish, feel free to pick off small amount of leaves from your grown plant.
Flowers can also be used and sprinkled over salads!
Preheat oven to 350°. Toast walnuts on a rimmed baking sheet, tossing once, until slightly darkened, 8–10 minutes. Let cool.
Heat broiler. Toss tomatoes with 2 Tbsp. oil on a rimmed baking sheet; season with salt. Broil, tossing once, until tomatoes are blistered and have released some of their liquid, 5–7 minutes. Let cool.
Pulse anchovies, garlic, lemon zest, red pepper flakes, and ½ oz. Parmesan in a food processor until finely ground. Add walnuts and half of tomatoes, then, with motor running, stream in ⅓ cup oil; process just until combined. Season with salt. Transfer pesto to a large bowl and stir in black pepper.
Cook pasta in a large pot of boiling salted water, stirring occasionally, until al dente. Drain, reserving ½ cup pasta cooking liquid.
Transfer pasta to bowl with pesto and add a splash of pasta cooking liquid. Toss, adding more cooking liquid as needed, until sauce coats pasta. Add basil and remaining tomatoes.
Divide among bowls; top with more Parmesan and black pepper and drizzle with oil.
Do Ahead: Pesto can be made 1 day ahead. Cover and chill.