Separate bulb of garlic into cloves. Peel and chop cloves. Heat oil and butter in a skillet over moderate heat. Add garlic and saute until fragrant. Remove from heat and let stand 20 minutes.
Cook spaghetti in plenty of boiling salted water until just done. Drain thoroughly, then transfer to a warm serving bowl. Reheat garlic and oil mixture, stirring in pepper flakes and anchovies. Add sauce to pasta and toss well. Season to taste with salt and pepper. Serve immediately.
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