Sticky Chocolate Cake

Name: Sticky Chocolate Cake
Ingredients: 1 cup (2 sticks) unsalted butter, plus more for pan; ⅓ cup (32 g) unsweetened Dutch-process cocoa powder (preferably Guittard Cocoa Rouge), plus more for pan; 2 oz. bittersweet chocolate (60%–70% cacao), broken or chopped into pieces; 5 large eggs; 1¾ cups (350 g) granulated sugar; 1 Tbsp. instant espresso powder; 1 Tbsp. vanilla bean paste or vanilla extract; 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt; 1½ cups (188 g) all-purpose flour; Powdered sugar (for dusting); Coffee ice cream (for serving; optional)