Stir together sugar and corn syrup in a 1-quart microwave-safe container. (A bowl or extra-large measuring cup with a handle would be ideal for safe handling.)
Microwave on high for 4 minutes. The mixture will be extremely hot. Stir in peanuts and microwave on high for 3 more minutes. Add butter and vanilla, blending well. Microwave on high for 1 minute more. Add baking soda and stir until foaminess begins to die down about 25 strokes.
Carefully pour the hot mixture onto an ungreased cookie sheet. Use a silicone spatula to empty the bowl and spread the candy out. Cool completely. Break into large pieces and store in an airtight container.
Recipe by Premeditated Leftovers™ at https://premeditatedleftovers.com/?p=32624