1 serrano chile, coarsely chopped, seeds removed if desired
2 cups cilantro leaves with tender stems (about 1 bunch)
1 cup (2 sticks) unsalted butter, room temperature
2 tsp. finely grated lime zest
2 tsp. kosher salt
5 lb. potatoes of mixed colors and similar sizes (such as sweet, purple sweet, russet, Yukon Gold), scrubbed
1 1/2 cups pomegranate arils (from 2 pomegranates)
Lime wedges and flaky sea salt (for serving)

Pulse chile and cilantro in a food processor until finely chopped.
Add butter, lime zest, and kosher salt and pulse until smooth.
Transfer to a sheet of parchment paper and roll into a 6"-long log.
Chill until firm, at least 2 hours and up to 3 days.
Preheat oven to 375F.
Arrange potatoes in an even layer on a rimmed baking sheet and cover tightly with foil.
Roast 40 minutes.
Remove foil (save for later!), turn potatoes, and continue to roast, uncovered, until largest potato is very tender when pierced with a paring knife or fork, 20–30 minutes.
Unwrap chile-lime butter and thinly slice crosswise.
Using two forks, tear potatoes (including skins) into 3"–4" pieces.
Transfer to a large (preferably warmed) platter.
Using your hands, crumble and scatter butter over potatoes (yes, use all of the butter).
Cover with reserved foil and let sit until butter is mostly melted, 3–4 minutes.
Top with pomegranate arils, squeeze lime juice over, and sprinkle with sea salt.