In large pot of boiling salted water, cook pasta for 8 to 10 minutes or until tender but firm. Reserving 1/2 cup (125 mL) cooking water, drain pasta and return to pot.
Meanwhile, in large skillet or Dutch oven, melt 1 tablespoon of the butter over medium heat; cook onion and garlic, stirring occasionally, for 5 minutes or until softened. Stir in spinach and basil; cover and cook for 2 minutes. Uncover and cook, stirring, for 2 minutes longer. Transfer to food processor. Add remaining butter, salt and pepper; puree until smooth. Add reserved pasta water; blend well.
Add spinach mixture to pasta along with 3/4 cup (175 mL) of the ricotta cheese, Parmesan cheese and lemon juice; toss to combine. Serve each with dollop of remaining ricotta; sprinkle with pine nuts.