The sweet, savory, and spicy condiment called Nam prik pao is the classic garnish for tom yum noodles, but it's too good to be relegated to one single use.
Set a fine-mesh strainer over a heatproof bowl. In a medium saucepan over medium-high heat, warm the oil and shallots, stirring frequently, until shallots are deep golden brown, 8 to 10 minutes.
☞ TESTER TIP: Keep a close eye on the shallots. Once they start browning, they color very quickly.
Using a slotted spoon, move the shallots to a second bowl. Add garlic to hot oil in saucepan and cook, stirring constantly, until golden brown, 1 to 2 minutes. Using a slotted spoon, dump the garlic into the bowl with the shallots.
Add the arbol chiles and half of the reserved seeds to the hot oil and cook, stirring constantly, until the chiles turn deep reddish brown, about 1 minute. Pour oil through the prepared strainer and into the bowl; reserve oil and add the chiles to the bowl with the shallots and garlic. Do not wash saucepan.
In a blender or mini food processor, blend the shallot mixture, sugar, and lime juice until a thick paste forms, 45 to 60 seconds, scraping down sides of container as needed. If the mixture isn’t blending well, drizzle in a little extra lime juice.
Return the paste to the now-empty saucepan, add the fish sauce and 2 tablespoons of reserved oil. Bring to a simmer over medium-low heat. Cook, stirring frequently, until the mixture is thickened and has a jam-like consistency, 4 to 5 minutes. Remove from the heat.
Season with extra lime juice, extra fish sauce, and salt, to taste. (Jam can be refrigerated for up to 1 month.)