Combine sugar, syrup, and water in a large deep kettle. Bring to a boil stirring to make sure all the sugars melt and nothing sticks to the bottom.
When the mixture reaches 260°F add butter, peanuts and continue stirring and cooking until the thermometer reaches 310°F
Remove from heat and add vanilla and soda. Stir very quickly as the mixture will become very foamy.
Immediately pour the mixture out onto the baking sheets.
After the brittle has hardened, break into a few large pieces. Put the brittle into large plastic bags so the shards don’t go flying all over the kitchen when breaking them up into smaller bite-sized pieces.
Store brittle in sealed jar, can or plastic bag.
Notes
Feel free to substitute other nuts in this recipe. You may want to chop very large nuts (like Brazil nuts) in 2-3 pieces before making.