In a large microwave-safe bowl, mix peanuts, sugar, corn syrup and salt. Cook on high for 6-7 minutes; mixture should be bubbly and peanuts lightly browned. Quickly stir in butter and vanilla; cook 2 to 3 more minutes. Add baking soda and stir quickly until mixture is foamy. Pour immediately onto a greased baking sheet. Let cool for 15 minutes or longer. Break into pieces and store in an airtight container.