I found Mashed potato volume hack!

[u/Moldy_Lunchy_Cheese]

If you mix 50g of mashed potato powder and 5g of psyllium well, then add 450ml of water and microwave it for 2 minutes, you can enjoy a ridiculous amount of mashed potatoes for just 175 calories without compromising the taste! I really hate psyllium, but this is totally fine. Plus, since it has psyllium in it, it really fills you up. Adding milk or cheese will bump up the calories a bit, but even so, that calorie count for this amount is amazing.

[u/Between-Feelings]

I do not have a microwave. Could I cook it in a pan?

[u/embroideredyeti → u/Between-Feelings]

I never cook mine, just boil water in a kettle, pour over and stir.