Step 1 Put the butter in a medium bowl and beat it with a wooden spoon until it turns soft and creamy. Stir in the lime zest, lime juice, salt, white pepper, chopped cilantro, garlic and chile flakes.
Step 2 Spoon onto a sheet of plastic wrap and roll into a sausage shape. Twist the ends of the wrap to seal the flavored butter. Chill until firm.
Step 3This makes a generous one-half cup butter, more than is needed for the remainder of the recipe; the butter will keep, covered and refrigerated, for up to 3 days.