Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes. (Firm or slightly undercooked risoni works best for this dish.) Drain, transfer to a mixing bowl.
Heat olive oil and butter in a large frypan over medium high heat, stirring to blend. Stir in garlic, basil and chilli flakes, and reduce heat to medium. Stir in pine nuts and cook until lightly browned. Add spinach, cover, and cook on low heat for 5 minutes, or until spinach is wilted.
Toss spinach mixture with risoni pasta. Serve with a drizzle of balsamic vinegar and a sprinkling of crumbled feta cheese and chopped tomatoes. Allow guests to adjust seasoning with salt, as needed.