Line 3 (9" x 5") loaf pans with multipurpose sealing wrap (we tested with Press 'N Seal); set aside. (Use disposable loaf pans from the grocery store, if desired.)
Place candies in a zip-top plastic freezer bag. Coarsely crush candies using a meat mallet or rolling pin. Set aside crushed candies, reserving 3 Tbsp. separately for topping.
Microwave white chocolate morsels in a large microwave-safe bowl at 70% power for 1 minute and 15 seconds. (Morsels will not look melted.) Stir morsels until melted. Microwave again at 15-second intervals, if necessary.
Add peppermint extract and larger portion of crushed candies to melted chocolate, stirring until evenly distributed.
Quickly spread melted white chocolate evenly in prepared pans; sprinkle with reserved 3 Tbsp. candies, pressing gently with fingertips.
Let stand 1 hour or until firm.
Peanut Brittle Candy Slabs: Melt white chocolate as directed in recipe above, gently folding in 1 1/2 cups crushed storebought peanut brittle and 1/2 cup creamy peanut butter; spread evenly in prepared loaf pans. Dollop 1 Tbsp. creamy peanut butter over candy mixture in each loaf pan; swirl with a knife.
Sprinkle 1/2 cup crushed peanut brittle evenly over candy in pans, pressing gently with fingertips.
