How to Make It
In a bowl, whisk 1/4 cup of the sweet chile sauce with 1/4 cup of water and 2 tablespoons of the fish sauce. Add the chicken; turn to coat. Cover and refrigerate overnight.
In a small saucepan, combine the remaining 1/2 cup of fish sauce with the palm sugar, cilantro, lemongrass and sambal oelek. Simmer over moderate heat until reduced to 1/2 cup, about 8 minutes. Strain the sauce through a fine strainer into a bowl. Stir in the remaining 1/2 cup of sweet chile sauce; let cool.
Spread the cornstarch in a shallow bowl. Remove the chicken from the marinade, scraping the excess back into the bowl. Dredge the chicken in the cornstarch.
In a large, deep skillet, heat 1 inch of oil to 350°. Fry the chicken at 300°, turning once, until golden and an instant-read thermometer inserted in the thickest part of each piece registers 160°, 15 to 18 minutes. Transfer the fried chicken to the sauce and toss to coat. Arrange the chicken on a platter and serve right away.