Step 1

Cook 3 medium ripe mangoes, peeled, coarsely chopped (about 4 cups), ⅓ cup (67 g) granulated sugar, 1 Tbsp. fresh lemon juice, and a pinch of kosher salt in a medium saucepan over medium heat, stirring often and smashing fruit with a wooden spoon, until thick and jammy, 15–18 minutes. Using an immersion blender (or transferring to a standard blender), blend until smooth; stir in 2 tsp. sumac. Let mango purée cool.

Step 2

Whisk 1 cup sweetened condensed milk, ½ cup plain whole-milk Greek yogurt or labneh, ½ tsp. vanilla extract, and a big pinch of salt in a medium bowl to combine, then stir in 1 oz. bittersweet chocolate, finely chopped.

Step 3

Using an electric mixer on medium-high, beat 2 cups heavy cream in a small bowl until stiff peaks form. Transfer 1 cup whipped cream to bowl with yogurt mixture and gently fold to combine. Scrape yogurt mixture into bowl with remaining whipped cream and gently fold to combine (be careful; you don’t want to deflate the cream).

Step 4

Transfer a third of cream mixture to a 9x5" loaf pan and spread into an even layer. Top with a third of mango purée and swirl to create ribbons and pockets of purée throughout cream mixture. Repeat process of layering and swirling 2 more times, dividing remaining cream mixture and purée evenly between layers. Smooth surface and cover tightly with plastic wrap. Freeze until solid, at least 8 hours.

Step 5

Let semifreddo sit at room temperature 10 minutes before scooping into bowls.Do ahead: Semifreddo can be made 5 days ahead. Keep frozen.