Grease a baking sheet and set aside. In a glass bowl, combine peanuts, sugar, syrup, and salt until well mixed.
Heat in microwave for 6 to 7 minutes on high until mixture is bubbly and peanuts are browned.
Stir in butter and vanilla; cook for 2 to 3 minutes longer. Quickly stir in baking soda, just until mixture is foamy.
Pour immediately onto greased baking sheet.
Let cool for 15 minutes or until set. Break into pieces and store in an airtight container.