Combine nuts and roasted garlic in a large bowl, coating the nuts with the garlic.
Spread mixture as evenly as you can in one thin layer on the parchment paper.
On medium heat in a small saucepan, add corn syrup, sugar and water. Attach candy thermometer to the side of the pot so the tip is inside the liquid but not touching the bottom of the pan. Do not stir.
Bring mixture to a boil, brushing down the sides of pot with a pastry brush dipped in cold water, if needed.
When mixture reaches 112ºC on a candy thermometer (approximately 10 minutes), check that it has reached softball stage (when you drop a bit of candy in cold water, it will form a soft ball, not a thread).
Stir in butter and salt and cook to 150ºC on a candy thermometer (approximately 10 minutes) or until it reaches hard crack stage (when you drop a bit of candy in cold water, it will form hard, brittle threads that crack when bent). Be careful not to burn yourself. Let candy cool in water for 1 minute to avoid burns.
Add baking soda and mix for approximately 1 minute. The mixture will foam with the baking soda.
Remove from heat and immediately pour hot sugar mixture over garlic/nut mixture on parchment- lined baking sheet. Working quickly and spread evenly with a spatula as best you can (this is easier with a kitchen partner
Wait for brittle to cool until firm. Once cooled, break into pieces and enjoy!
*Toss peeled garlic generously in olive oil and roast in oven, uncovered on parchment paper, at 175ºC for approximately 1 hour, until deeply golden.
Be sure to have a candy thermometer, parchment paper and pastry brush on hand when making this recipe.