Line 2 sheet pans with silicone baking mats or parchment paper.
Slice croissants in half horizontally.
Heat half and half, sugar and salt over medium low heat, stirring until sugar and salt are completely dissolved. Pour into pie plate or shallow bowl. Dip each croissant piece into the milk mixture, flip to coat both sides completely.
Use your fingers to gently squeeze the croissant so excess liquid comes out. The croissant should be soaked but not dripping. Place on prepared pan. Use one pan for larger pieces, the other for smaller pieces, as they will cook for different times.
Repeat until all croissant pieces are done, spacing them evenly on the sheet pans. Sprinkle each piece lightly with cinnamon sugar.
Bake for 45 minutes. Rotate pans halfway through. Check the brittle at 45 minutes, the smaller pieces will be done before the larger pieces, which will need an additional 5-10 minutes. The brittle is done when deeply browned, fairly firm but not crisp to the touch. As it cools, it will become crispy with very little give.
If after cooling 10 minutes it feels soft, bake another 5 minutes. Cool slightly on sheet pan then remove from silicone baking mat to a cooling rack to cool completely.
Store in airtight container. *Make cinnamon sugar by mixing ½ cup granulated sugar with 1 tablespoon cinnamon. Serving suggestion: Top brittle with a dollop of crème fraiche and sliced strawberries glazed with Unicoi Preserves Strawberry Vanilla Spread.