Add all ingredients to a small saucepan and heat over medium.
Whisk to combine and let simmer for a few minutes to combine and thicken slightly.
Season with salt and pepper to taste.
Tuna Casserole Assembly
Preheat oven to 350F/180C.
Steam broccoli florets until just tender, don't overcook as they will cook a little more in the oven.
Arrange broccoli in an oven-proof dish, sprinkle over tuna evenly. Pour over the prepared cheese sauce and sprinkle with grated cheese.
Bake for 15-20 mins until golden on top and bubbling. Allow to cool for 5 mins before serving.
Video
Notes
Keto chicken casserole - If you are not a fan of tuna or have some leftover shredded chicken, this recipe also works really well with shredded chicken in place of the tuna.
Broccoli alternatives - You can substitute other cooked veggies in place of the broccoli. We like a combination of steamed broccoli and cauliflower.
Make ahead - If you like to meal prep you can make the cheese sauce and steam the broccoli ahead of time and then assemble the casserole prior to cooking.
Storage - The cooked keto tuna casserole will keep in the fridge for 4-5 days. We like to store it in pyrex storage containers. It reheats well in the microwave or covered in the oven.
Serving suggestions - As this meal contains a lot of protein and veggies we find it is a complete meal. You can also serve it with additional veggies or a side salad if you prefer.
NOTE: THIS IS BASED ON THE INGREDIENTS WE USED, NUTRITIONAL INFORMATION MAY VARY DEPENDING ON THE INGREDIENTS USED.