FOR THE COOKIE CAKE: – 1 & 1/2 cups (180g) all-purpose flour – 1 & 1/2 teaspoons cornstarch – 1/2 teaspoon baking soda – 1/4 teaspoon salt – 1/2 cup (113g) unsalted butter, melted and slightly cooled – 1/2 cup (100g) firmly packed light brown sugar – 1/4 cup (50g) granulated sugar – 1 large egg – 2 teaspoons vanilla extract – 1 cup semisweet chocolate chips FOR THE FROSTING: – 1/4 cup (56g) unsalted butter, softened – 1 cup (110g) confectioners' sugar – 2 tablespoons unsweetened cocoa powder – 1/2 to 1 tablespoon heavy cream – 1/2 teaspoon vanilla extract – pinch of salt – sprinkles, for garnish