In a covered 1-1/2-qt. microwave-safe glass dish, microwave the walnuts, sugar, corn syrup and salt on high for 2-1/2 minutes. Stir; cook 2-1/2 minutes longer. Stir in butter and vanilla. Cover and microwave on high for 1-1/4 minutes. Add baking soda; stir quickly until lightly foamy. Immediately pour onto a lightly buttered baking sheet; spread until very thin. When cool, break into small pieces. Store in an airtight container at room temperature.
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