NOTE: 1 1/2 teaspoons of red Sichuan peppercorn will give the brittle a forceful punch, which is what the original intended. If you are more of a Sichuan peppercorn-beginner, you can start with 1 teaspoon first and see how that suits you. Moreover, the recipe is based on the assumption that store-bought salted peanuts are usually lightly salted. If for some reason your roasted salted peanuts are potato chips salty, you might have to reduce the 1/2 teaspoon of salt to 1/4 teaspoon.
Preheat the oven on 350º F (175º C).
Finely crush the sichuan peppercorn in a stone mortar or spice-grinder. In a large bowl, first fold 2 tbsp of beaten egg white and salted peanuts together until evenly coated, then add the crushed peppercorn, chili flakes and salt, and fold again until evenly mixed. Spread over a parchment paper-lined baking sheet and bake in the oven for 6 ~ 7 minutes, scrambling them with a fork once in between, until the surface of the peanuts are dry (remember, the peanuts were already roasted. we are just applying more flavours). Let the peanuts cool COMPLETELY inside the baking sheet.
Cover the peanuts with 2 layers of plastic wrap, then smash them with a hammer to crush about 1/3 of them into small pieces, leaving the rest of the peanuts whole or in large pieces. Transfer the peanuts to a bowl and mix with the baking soda. Put the unsalted butter on top (this will make it easier to add the peanuts to the caramel). Set aside. Apply a little bit of cooking-spray over a sheet of parchment paper and a spatula, or rub both with a bit of oil. Set aside.
In a large pot (the caramel will bubble and foam later so you’ll want enough room for this to happen), add granulated sugar, water, corn syrup and salt, and cook over medium-high heat. Stir gently with a wooden spoon only occasionally, and cook until the mixture turns from completely clear to a light amber color. This will take very roughly 15 to 20 minutes, but watch carefully. Once the sugar turns light amber, turn off the heat immediately. Give it a couple more seconds (the color will continue to darken very fast), then add the peanuts with the baking soda and unsalted butter. Quickly stir the mixture with a wooden spoon until it’s evenly mixed, and that the foaming has subsided.
Pour the mixture onto the oiled parchment paper and spread it with the oiled spatula. If it’s cooling too quickly and becomes unspreadable, cover it with another piece of parchment paper and a kitchen towel on top (so that you do not burn your hands), and press it down with your hands. Once flattened, chill in the fridge for 15 minutes to cool down.
Shatter the brittle with a hammer or cut with a knife. Keep in a container for 1 week.