Brown Butter Couscous With Spring Vegetables

Name: Brown Butter Couscous With Spring Vegetables
Ingredients: 5 tablespoons butter, divided; 1 cup instant couscous (see Step 2 for substituting pearl couscous); 1/2 cup frozen peas; 2 teaspoons sumac, divided, plus more to taste (see author note); 1 pinch kosher salt, plus more to taste; 1 pinch freshly ground black pepper, plus more to taste; 1 bunch radishes, trimmed (see author note); 4 cups baby spinach or arugula; 1/3 cup sliced almonds (or walnuts, pine nuts, or pistachios); 2 tablespoons dried currants (or raisins or chopped dates); 2 ounces crumbled feta (or crumbled chèvre or torn mozzarella); 1 small lemon, for juicing (or white or red wine vinegar)