Remember all microwaves vary so you may need to adjust your time by 15 seconds. If the first batch comes out to soft then you know you didnt cook it long enough. After you make the first batch it gets really easy and fast to make.
In a large microwave safe bowl stir peanuts, sugar, syrup and salt together. Be sure to mix them well. (rubber spatula works really well).
Microwave for 3 minutes 45 seconds to 4 minutes.
Stir with a metal spoon so it doesnt stick. Stir it quickly so it doesnt have time to cool.
Microwave 3 1/2 to 4 more minutes.
Stir in butter.
Microwave 2 more minutes.
Stir in vanilla and dont panic when it steams and turns brown.that is what you want.
Add baking soda and stir quickly until is gets light and foamy.
Immediately pour onto a lightly buttered baking sheet and spread to about 1/4 inch thick.
break into pieces and store in an airtight container.