High calorie food?

[PurpleKat]

So I've spoken to my vet today about my elderly hamster and her impacted cheek pouch.
He discussed that due to my 2 year old dwarf hamster weight loss he wouldn't be able to remove it easily.
She's about 35g and you can feel her spine.
He did suggest a high-calorie diet to bulk her up before he did any serious intervention.

She does have her teeth but I'm feeding her more softened food and pureed as she is a slight bit dehydrated. Also, she eats the soft food immediately instead of pouching the food. And some of her regular hamster food.

She's quite happy and is active, runs a little bit on her wheel and rummages around her enclosure.

I'm giving her porridge, smushed banana, boiled veggies as a puree (like baby food) .
Any ideas for high calorie food thou to fatten her up a bit?