think of your veg and salads as a vehicle for cheese, butter and mayo.
add coconut cream to curries
choose fatty meat options like belly pork, chicken in cream sauces, fattier cuts of meat. Leave the skin on chicken. Don't trim pork chops.
look at low carb fat bomb recipes
snack on egg mayonnaise instead of hard boiled eggs
buy streaky bacon instead of back bacon
eat avocados
add in nuts and pate which are both excellent combinations of fat and protein
nut butters can be eaten by the spoon. no need for bread or crackers
desserts of berries and cream, chocolate mousse, coffee mousse, etc.
and drinks.
it isn't just bullet proof coffee that works.
you can also make hot chocolate with cocoa powder, cream and sweeteners. and if you let it go cold then it is chocolate milk.
you could make strawberry or raspberry 'milk' in the same manner, by blitzing up strawberries, ice water and cream.
golden milk (turmuric milk) is often made with nut milks, but you can do it like a bulletproof coffee if you like
where there is a will, there is a way.
But I strongly suggest that you ease into higher levels of fat intake. Don't do something silly like try and add 1,500 calories of extra food in a singleday. That will just make you feel queasy and ill. Do it gradually over several days or weeks. Just adding a big handful of roasted peanuts before each meal would go a long way to stopping your weight loss.
Also IMPORTANT:
Some people just don't find that fat will add weight, UNLESS they get the carbs right. In other words, you may need to add back in some carbs (the amount will vary from person to person) in order to allow weight gain. After all, insulin is the fat storing hormone, so we need it to store fat. If you have cut carbs so hard that there isn't enough insulin around, then no amount of fat intake is going to help.