Combine 1/2 cup olive oil, 1/2 cup fish sauce, 1 tbsp kosher salt, 4 stalks lemon grass stalk, chopped into 1" pieces, 1 small bunch cilantro stems chopped, 1/4 cup brown sugar, 1/4 cup whole black peppercorns, 3 tbsp light soy sauce, 2 tbsp coriander seeds, and 8 cloves garlic in a food processor. Pulse contents until it forms a coarse purée.