Step 1

Place a rack in middle of oven; preheat to 350°. Lightly butter pan; line with a round of parchment paper cut to fit just inside pan. Pulse nuts in a food processor until finely chopped. Add sugar and salt and pulse again to combine. Drizzle in melted butter and pulse until nuts begin to clump together and mixture looks sandy. Using your hands, firmly and evenly press mixture into bottom and up sides of pan (it doesn’t need to come all the way up the sides). Bake crust until golden brown, 20–25 minutes. Let cool.

Step 2

Place chocolate in a medium bowl. Heat cream in a small saucepan until just beginning to simmer; immediately pour over chocolate. Let sit, undisturbed, 5 minutes. Add butter and mix with a heatproof rubber spatula until smooth and glossy. Scrape ganache into crust and smooth out any bubbles. Chill, uncovered, until set, at least 1 hour.

Step 3

Remove tart from pan; sprinkle sea salt over. Slice into wedges with a hot knife.

Step 4

Do Ahead: Tart can be made 1 day ahead. Cover and keep chilled.