Possibly the chemistry & method in this preparation will be successful in your kitchen:
Per ½ lb of nuts (I’ve used pecans & peanuts – but, alas never the pricey macadamias!), combine the nuts w/ 1 cup each white granulated sugar & light corn syrup. Cook in saucepan until mixture reaches hard-crack stage (295°). Remove pan from heat, stir in 1 Tbsp baking soda; stir down the foam and then spread the mixture onto an oiled baking sheet or marble slab.. Of course, for evenly sectioned pieces, I suppose you could spread it on parchment paper bordered by perimeter bars, and score it, much like for taffy. However, with brittle you’ll want to stretch it out for a thinner setting.
Alternatively, one can produce a top-grade caramel-cashew brittle:
2 cups granulated sugar
8 fl. oz. light corn syrup
8 fl. oz water
½ lb cashews
1 oz. butter
1 tsp vanilla extract
1 tsp soda
Note: Butter & baking soda ensure that your brittle will be opaque, rather than cheaply clear. Melt first 3 ingredients; stir in nuts at 265°. (Control crystallization accordingly.) Cook, stirring often, till mixture reads 310°. Add butter & vanilla. Incorporate soda. Pour onto slab. Wearing those heat-proof neoprene gloves, use scraper to loosen & stretch brittle mixture. When, completely cool, break into pieces.
Btw, use the flaked or ribbon coconut, instead of shredded in your recipe.