Bring a large pot of water to a boil. Add penne and boil for 10 minutes or according to package directions. Meanwhile, in a heavy 12-inch skillet heat butter and olive oil until foamy. Add pine nuts and saute, stirring until they turn golden. Add garlic and saute for a minute to release the aroma. Add spinach and toss together just until wilted. (You might need to do this in two batches). Season with salt and pepper. Add a tablespoon or so of water to get spinach steaming. Drain pasta and toss with wilted spinach in a large serving bowl.