Preheat the oven to 325 degrees F (165 degrees C). Grease an 8-inch cake pan and dust with almond flour.
Whisk almond flour, honey, walnuts, eggs, cocoa powder, coconut oil, and vanilla together in a large bowl. Pour into the prepared pan and smooth top.
Bake in the preheated oven until center is set and edges pull away from the sides of the pan, 20 to 25 minutes. A toothpick inserted into the center should come out clean or have a few moist crumbs attached.