Source: Hazel's Candies: Copper Kettle Trade Secrets - Hazel Holen
3/4 cup water
1 1/2 cups granulated sugar
1 1/2 fluid ounces corn syrup
2 teaspoons salt (if nuts are unsalted)
Dab of lecithin on the tip of a table knife
3 tablespoons butter
1 1/2 teaspoons vanilla extract
12 ounces warm, roasted cashews
Oil kettle sides. Add water and bring to a boil; set off heat. Add sugar and stir to melt. Mix in corn syrup, lecithin and salt. Stir on medium to high heat, bringing to a second boil.
With kettle lid on, steam for 3 minutes, then wash around cook line with a pastry brush dipped in cold water. Put the thermometer in the syrup without additional stirring. When batch begins to thicken, turn heat to medium/low and cook to 280 degrees F or soft crack.
At 280 degrees F, gently mix in butter. Watch for a deep caramel color or hard crack at 295 degrees F. Quickly remove from heat before candy begins to smoke.
Add vanilla and nuts, mixing well. Immediately scrape the candy into a mound on a warm buttered marble slab or 18- to 23-inch bun pan, keeping it confined to a pile for heat containment. With a chef's knife or spatula, turn brittle over for even distribution of syrup. Using bent-tine table forks, pluck out silver dollar-size clusters from the mass.
This batch sets up quickly, so work with haste, turning the candy mound occasionally. When small candy clusters are cool, place in plastic bag.