How to Make It
Preheat oven to 400°F. Combine mozzarella and cream cheese in a large microwavable bowl. Microwave on HIGH just until melted, about 1 minute. Stir to combine, and cool slightly, about 5 minutes. Stir together almond flour, oat flour, xanthan gum, and baking soda in a separate large bowl; set aside.
Combine egg and melted cheeses in the bowl of a food processor. Process until combined, about 20 seconds, stopping to scrape down sides of bowl as necessary. Add flour mixture, and process until dough forms a ball, about 20 seconds. (Mixture will be slightly sticky.) Remove dough from food processor, and wrap with plastic wrap. Chill 15 minutes.
Unwrap dough, and place on a clean work surface. Cut dough evenly into 6 pieces.Roll each piece into a 6-inch- long log. Pull together ends of each log to form a circle, and pinch to seal. Place on a parchment paper-lined baking sheet, and brush evenly with melted butter. Sprinkle each bagel with poppy seeds, sesame seeds, or minced onion.
Bake until bagels are golden brown and cooked through, about 12 minutes.