Line a 12x16x1/2-inch baking sheet with parchment.
In a large saucepan, stir together the sugar, butter, corn syrup, and 1/2 cup plus 2 tablespoons water until the sugar is thoroughly wet. Cook the mixture over medium-high heat, keeping an eye on it at all times. If it starts to foam up to the top of the pan, lower the heat slightly.
When the mixture reaches a deep golden color (this will take 10 minutes or more) remove it from the heat, and stir in the Cholula and the pepitas with a wooden spoon (be careful, as the caramel will bubble fiercely).
Pour the mixture out onto the prepared sheet pan, and use the back of the spoon to spread it evenly over the pan before it begins to harden.
Cool completely, then break it into bite-size pieces with the back of a knife or other blunt object.
Store the brittle at room temperature, in an airtight container, for up to two weeks. To keep the pieces from sticking together, separate layers of brittle between sheets of parchment paper.