Harissa Sweet Potato Tarte Tatin

Name: Harissa Sweet Potato Tarte Tatin
Ingredients: 1 sheet frozen puff pastry (one 14-oz. package or half of a 17.3-oz. package), thawed; All-purpose flour (for surface); 3 Tbsp. unsalted butter, room temperature; 2 Tbsp. plus 2 tsp. light brown sugar; Kosher salt; ⅓ cup harissa (such as Mina); 1 tsp. ground cumin; 2 medium sweet potatoes (about 1 lb.), peeled, sliced into ¼-thick rounds; 1 small red onion, thinly sliced; ½ cup white wine vinegar; 1 Tbsp. coriander seeds; Flaky sea salt