Combine the lime juice, rice vinegar, and sugar in a small saucepan and bring to a simmer, swirling the pan until the sugar dissolves. Stir in the lemongrass and lime leaves and set aside until cool. Strain the solids and discard.

In a small sauté pan, heat 2 teaspoons of the oil over medium heat and add the shallots and ginger. Cook, stirring frequently, until softened, 2 to 3 minutes. Add the kumquats and the reserved lime juice mixture and bring to a simmer. Cook until slightly thickened, 1 to 2 minutes. Stir in the Thai chile and kosher salt and remove from the heat; cool to room temperature. Chutney may be made up to several days in advance and refrigerated in a nonreactive container until ready to serve. (If made in advance, return to room temperature before serving.)

**Note:  If kumquats are unavailable, you can substitute either sour oranges or key limes. Cooking time and sugar amount may need to be adjusted slightly.

Place the chicken thighs in a shallow bowl or in a plastic resealable food storage bag.

In a mortar, combine the chopped cilantro, garlic, crushed red pepper, and palm sugar and using a pestle, pound to make a uniform paste (it’s ok if it’s still a bit chunky). Transfer to a bowl and stir in the remaining 2 tablespoons of oil and the fish sauce. Pour the marinade over the chicken and move the pieces around, making sure that they are evenly coated with the marinade. Refrigerate for up to 4 hours, or allow to marinate at room temperature for 1 hour.

Preheat a grill or grill pan to medium-high.  Cook the chicken until nicely marked on both sides, cooked through, and a thermometer inserted into the thickest portion of the thighs reads 165 degrees F.

Serve the chicken hot or warm over sticky rice, with the Lemongrass-Kumquat Chutney spooned over the top and garnished with the cilantro sprigs.