Line a 9×9-inch baking pan with parchment paper that fits your air fryer.
In a blender or food processor, blend the strawberries until smooth. Strain through a fine mesh sieve to remove the seeds. Set aside.
9 ounces strawberries
In a medium bowl, whisk together the flour and salt. In a saucepan over low heat, melt the butter and chocolate together, stirring until smooth.
1¾ cups all-purpose flour, ½ teaspoon salt, 1½ cups butter, 12 ounces chocolate
In a large bowl, use a hand mixer to combine the granulated sugar, brown sugar, eggs, and vanilla extract until smooth. Remove the saucepan from the heat and pour it into the mixture, mixing well. Add the flour mixture and gently fold until just combined. Do not overmix.
1½ cups granulated sugar, ⅔ cup light brown sugar, 6 large eggs, 1½ teaspoons vanilla extract
Pour the batter into the prepared pan and spread it evenly. Drizzle the strawberry puree on top and swirl with a knife to create a marbled pattern.
Bake in the air fryer at 400°F (200°C) for 15 minutes, rotating the pan halfway through, until the edges are set and a toothpick inserted in the center comes out with a few moist crumbs.
Let cool completely in the pan before slicing and serving.