1/2 cup half & half
3/4 cup sugar
1 tsp kosher or coarse seasalt
Heat the oven to 300°F. Line 2 sheet pans with parchment or silicone mats.
Using a serrated knife, slice the croissants—horizontally, as if you were making a sandwich—into thin slices (figure 1/4- to 1/2-thick). Depending on the croissant, you should be able to get about 3 pieces out of each.
Heat the half and half on the stove over low heat until very warm. Turn off the heat and add the sugar and salt. Stir until the sugar has totally dissolved. Pour into a shallow bowl.
Using your hands, dip one croissant piece in the syrup and flip over to completely coat. Gently squiiiiiish the soaked piece between your fingers to squeeze out some excess. (It should still be soaked, just not dripping.) Transfer to a lined sheet pan.
One sheet pan will be for bigish pieces (roughly 5 x 3 inches). The other will be for smallish pieces (roughly 3 x 2 inches). These cook for different amounts of time, so dividing them will come in handy soon!
Repeat with the remaining croissant pieces, spreading them out on the sheet pans evenly. Sprinkle each croissant piece with a little sugar.
Bake for about 45 minutes, rotating the sheet pans halfway through: top to bottom, front to back. At the 45-minute mark, check in with the brittle. The smallish pieces are probably done—remove that sheet pan from the oven. The bigish pieces probably need another 5 to 10 minutes. The brittle is done when it is deeply browned, with the outside the color of dark caramel and the inside, honey. It shouldn’t be crispy to the touch, but fairly firm, with very little give. (Just be quick and careful when touching, since the sugar is hot.) When the brittle cools, it should be completely crisp, with no give at all. If it has cooled for 10 to 15 minutes and still feels softish to the touch, just continue to bake for another 5 minutes, then check again.
Cool on the sheet pan until you can easily remove the brittle. The easiest way to do this is slowly peel the parchment away from the brittle, not the brittle away from the parchment. Transfer to a cooling rack to cool completely.