You would like to make Chardonnay Peanut Brittle but your question is when would you add the Chardonnay and would it replace the water in the recipe?

You should add the Chardonnay towards the end of the cooking process, just before you pour the mixture onto the baking sheet. It can replace some or all of the water in the recipe, but be mindful of the liquid ratio to ensure the brittle sets properly. Make sure to allow the alcohol to cook off slightly so that the flavor concentrates without being overly wet.