Cut the chicken into even pieces if needed, then toss with soju, ginger, garlic, salt, and pepper. Let it sit 20 to 30 minutes at room temperature, or up to overnight in the fridge.

Beat the egg into the marinated chicken so every piece is coated, then dredge each piece in potato starch, pressing gently so it sticks in a rough, even layer. Shake off the excess.

Heat the oil in a heavy, deep pot to 325°F / 163°C. Fry the chicken in batches of 5 to 6 pieces, without crowding the pot, for 8 to 9 minutes, until just cooked through (165°F / 74°C internal).

Lift the chicken onto a wire rack, not paper towels, and let it rest 8 to 10 minutes while you fry the remaining batches.

While the chicken rests, combine the gochujang, ketchup, rice syrup, soy sauce, brown sugar, garlic, ginger, and gochugaru in a small pan. Simmer over low heat 5 minutes, stirring, until it coats a spoon and holds a line when you drag a finger through it. Take it off the heat and stir in the sesame oil.

Raise the oil to 350-375°F / 175-190°C. Fry each batch again for 90 seconds to 2 minutes, until deep golden and audibly crackling when tapped with tongs.

Drain briefly on the rack, then toss the hot chicken in the warm glaze for no more than 20 to 30 seconds — fold rather than stir, just enough to coat every piece.

Scatter with sesame seeds and serve immediately, while the crust is still at its crispest.