Combine the half and half, nibs and vanilla in a medium saucepan. Warm over medium heat, swirling occasionally, until steaming and small bubbles form around the sides of the pan. Cover and steep for 30 minutes.
Pour the cold cream into a bowl or quart-sized measuring cup and set a fine mesh strainer over the bowl.
In a medium bowl secured on a damp towel, whisk together the yolks, sugar and salt. Re-warm the half and half until steaming again, then gradually pour it into the yolks, whisking constantly. Return the mixture to the pot, place over medium-low heat, and cook, stirring continually with a heat-proof rubber spatula, until the mixture begins to 'stick to' (form a film on) the bottom of the pot, or measures 170º on an instant read thermometer. Immediately pour through the sieve and into the cold cream, pressing on the nibs to extract any liquid. Optionally chill the mixture in an ice bath. Refrigerate at least four hours or up to a couple of days.
Spin the mixture in an ice cream maker until the texture of a thick milkshake, then mix in the candied nibs (below.) 'Cure' in the freezer for at least an hour or until firm enough to scoop.
Spread the nibs on a small baking sheet and toast in a 300º oven or toaster oven until just fragrant, 2 - 3 minutes. Place in a small bowl to keep warm and have at the ready.
Measure out the butter and salt and place it near the stove with the nibs. Line a baking sheet with parchment paper or a silpat (silicone baking mat.) Have a heat proof rubber spatula handy.
In a small saucepan, combine the water and corn syrup. Place the sugar in the center of the liquid so that it doesn't get on the sides of the pot, and gently moisten with your fingers. Place the pot over medium-high heat and cook until the sugar turns to an amber caramel, tilting the pan gently if the sugar colors unevenly, brushing down the sides of the pot with a wet pastry brush if crystals begin to form. Immediately add the butter and salt, swirl to melt, then add the nibs. Quickly stir with the spatula to coat, and scrape out onto the silpat. Spread the nibs as thinly as possible, then, as they begin cool, carefully use your fingers (don't burn yourself!) to pull the nibs into thin, amorphous shapes. Let harden, about 10 minutes. Reserve some bits for garnish if desired, then break up the rest into clumps of 5 or so nibs. Freeze for 10 minutes or so before adding to the ice cream.
The candied nibs can be kept at room temperature for a few days (the sugar may begin to soften) or in the freezer for up to a few months.