To make the gelato custard: In a medium-size bowl, stir together the sugar, egg yolks, vanilla and corn syrup to blend thoroughly.
In a heavy, medium-size saucepan, bring the half-and-half just to a simmer.
Gradually pour the warm half-and-half into the yolk mixture, stirring constantly.
Return the blended mixture to the saucepan.
Using a wooden or rubber spatula, stir the mixture over medium-low heat until custard thickens and leaves path on back of spatula when finger is drawn across, about 10 minutes (do not boil).
Strain the custard through fine-mesh sieve (Do NOT skip this step) into a bowl.
Cool in ice bath, then cover and refrigerate until cold.
Process the cold custard in an ice cream maker according to manufacturer's instructions.
To make the brulee crunch: Line a baking sheet with foil and generously butter the foil.
Or use the Reynold's"Release" foil, or use a Silpat sheet or other silicone coated baking mat.
In a heavy, medium-size saucepan, over medium-low heat, stir together the sugar and water until the sugar dissolves.
Increase the heat and boil the mixture without stirring until it becomes amber colored, brushing down the sides of pan with a wet pastry brush to remove sugar crystals and swirling the pan occasionally to cook evenly.
(About 10 minutes will be required to achieve an amber coloring.) Remove the pan from the heat.
Stir in the baking soda and immediately transfer the caramel mixture to the buttered baking sheet (or other sheet, as above).
Allow the caramel to cool completely, and break it into small pieces to make the brulee crunch.
Swirl 3/4 of the crunch into the gelato, then freeze gelato until firm.
Sprinkle servings with remaining crunch before serving.