Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with parchment paper.
Spread pecans onto a baking sheet and sprinkle sea salt and blackening seasoning over pecans.
Bake in the preheated oven until pecans are toasted and fragrant, 5 to 6 minutes. Remove from oven and cool pecans.
Place chocolate chips in the top of a double boiler over simmering water; gradually add unsweetened baking chocolate and stir. Add vanilla extract and heat until chocolate is melted and smooth, 5 to 10 minutes. Mix 1/2 of the pecans into the melted chocolate.
Pour chocolate mixture onto the prepared baking sheet and sprinkle remaining pecans over chocolate mixture. Cool to room temperature, about 30 minutes. Cover with plastic wrap and refrigerate until set, at least 1 hour. Break into pieces.