Combine crumbs and butter, and press mixture in bottom of 8-inch springform pan, three inches deep. With electric mixer, beat cream cheese and sour cream until smooth, then add sugar and flour. Beat in lemon juice and vanilla, then egg yolks, one at a time, and stir in nuts. In another bowl, beat egg whites with cream of tartar and pinch of salt until they hold stiff peaks, then fold into cream cheese mixture gently and thoroughly. Spoon into pan and bake in a 275 oven for 1 hour, 15 minutes, or until firm in center. Let cool in pan on a rack and chill, covered loosely, for at least 6 hours.

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