Spaghetti With Smothered Peas

Ingredients

• 3/4 teaspoon fine salt, divided, plus more as needed
• 5 tablespoons olive oil, divided
• 1/2 large sweet onion (6 ounces total), diced
• 2 cloves garlic, peeled and smashed
• 1 pound shelled tender fresh peas or frozen peas (3 3/4 cups; no need to defrost if frozen)
• 1 cup low-sodium chicken or vegetable broth
• 1/2 teaspoon freshly ground black pepper, divided, plus more to taste
• 12 ounces spaghetti, preferably whole grain
• 1/4 cup freshly grated pecorino Romano cheese
• 1/4 cup fresh basil leaves, cut into ribbons