I like to call chaffle sandwiches chaffwiches, it might never take off, but it gets the point across. Keto beef and cheddar chaffwich is loaded with flavor, whether you eat it open-faced or as a hearty two-handed sandwich.

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Making this is as simple as 1, 2, 3, make your chaffles, sautee the onions, then assemble and broil.
I use leftover roast beef, sliced thin, but sliced beef from the deli counter works just as well.
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Chef Jenn’s Take on Beef and Cheddar Chaffwich
Make the chaffles ahead of time to save real time, they freeze great and reheat well in the toaster or back in the waffle maker.
Sautee the onions in oil until translucent, about 4 to 5 minutes, and skip them entirely if you are doing strict keto. Lay the chaffle flat, spread on the mayo, then top with the roast beef, cheese, and onions. Broil for 2 to 3 minutes, until the cheese melts. Use my own Keto Roast Beef sliced thin, or sliced deli beef works just as well. Sharp cheddar cheese really enhances the flavor here.
Swap the mayo for Horsey Sauce to make this more like a certain roast beef chain’s sandwich, or use grainy mustard instead. Top it with sauteed mushrooms and peppers for a Philly-style version if you want something different.
For reheating, the broiler warms the beef and melts the cheese at the same time. You can also wrap it in foil and heat it in a 325 degree oven for about 10 minutes, flipping halfway through. The microwave risks overcooking it, so use 20-second intervals if you must. Freeze the components separately rather than the assembled sandwich.

What You’ll Love About Beef and Cheddar Chaffwich
- Ready in about 20 minutes, real lunch or dinner speed.
- Loaded with flavor, works open-faced or as a full two-handed sandwich.
- A great way to use up leftover roast beef.
Ingredients
- 2 of your favorite chaffles – Or 1 if you’re going open-faced.
- Sliced beef – Leftover Keto Roast Beef, sliced thin, or deli-sliced beef.
- Sliced or shredded cheddar – go for sharp cheddar for maximum flavor
- Onions – Sliced. Skip for strict keto.
- Mayonnaise – Optional. Horsey Sauce or grainy mustard work as substitutes.
How to Make Beef and Cheddar Chaffwich
Scroll down for the full recipe card with exact measurements and printable instructions.
Heat the oil in a small skillet over medium heat and add the onions. Sautee until translucent, about 4 to 5 minutes. Lay one chaffle on a flat surface and spread on the mayonnaise. Top with the roast beef, shredded cheese, and onions. Broil for 2 to 3 minutes, or until the cheese is melted.
Make It A Meal
I’m a big fan of soup and sandwich combos, this pairs beautifully with Cream of Mushroom Soup. For a salad, Cobb Salad with Ranch Dressing is another easy, tasty option.
If you love this format, French Dip Chaffwich is another great sandwich to add to your rotation.
Storage
Freeze the components separately rather than the whole assembled sandwich. Chaffles freeze well tightly wrapped, and the beef will also freeze if wrapped tightly. Thaw and reheat what you need.
Frequently Asked Questions
Topping this sandwich with onions and then melting the cheddar under the broiler should warm up your roast beef enough. Or, you can wrap it tightly in foil and heat it in a low oven (about 325-F) for about 10 minutes, switching the slices around about halfway through. Heating it in the microwave is likely to overcook it, so if you do use the microwave, just do it in 20 second intervals.
Heck yes. A great source of protein, roast beef is on the leaner side so you may need to add more fats. But yes, it’s a great pick on a keto diet.
I wouldn’t freeze the whole thing together, but rather freeze the individual components. Making chaffles ahead of time is a great time-saver. Freeze them tightly wrap then just thaw and reheat what you need. The beef will also freeze, if you wrap it tightly.
Beef and Cheddar Chaffwich
Ingredients
- 2 chaffles or 1 if you're going open-faced
- 1/2 tablespoon avocado oil
- 1/4 cup sliced onion
- 1 tablespoon mayonnaise
- 4 ounces roast beef cooked
- 1/4 cup cheddar cheese shredded
Instructions
- In a small skillet over medium heat, heat the oil and add the onions. Sautee the onions until they're translucent. About 4-5 minutes.
- Lay one chaffle on a flat surface and spread on the mayonnaise. Then, top it with the roast beef, shredded cheese, and onions.
- Pop it under the broiler for 2-3 minutes or until the cheese is melted. Enjoy!
Notes
Recipe Card Tips
- Make the chaffles ahead of time, they freeze well and reheat easily in the toaster or waffle maker.
- Use sharp cheddar specifically, it really enhances the flavor of this sandwich.
- Skip the onions if you’re doing strict keto.
Nutrition
A Note on Nutritional Information
Nutritional information for this recipe is provided as a courtesy and is calculated based on available online ingredient information. It is only an approximate value. The accuracy of the nutritional information for any recipe on this site cannot be guaranteed. Erythritol carbs (sugar substitutes) are not included in the carbohydrate counts as they have been shown not to impact blood sugar, and they have zero calories and zero carbs. Net carbs are the total carbs minus fiber.








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Now this looks delicious! I definitely need to make this happen in my life asap. 😉
Wow, this looks amazing!! I am definitely adding this to my weekend meal ideas. Thank you so much for the recipe 🙂
This was everything a gourmet sandwich should be, and then some! So delicious and hearty; easily, a new favorite way to enjoy roast beef!
Yummy! I can’t wait to try this! Looks so delicious and very tasty! Excited to share this with my family!
fyi – Keto bread is now available by Orowheat, my main goto for sammiches, sometime I use low-carb tortillas for sammiches & wraps! There are several brands on the store shelves now, but the Mission ones r my fav. I would definitely make this beef & cheddar with one of these keto friendly products!
Thanks for the tip! ~Jenn