Use double the amount of oil and butter than you normally would when cooking.
Use olive oil as a condiment, drizzle it on top of your veggies, spag bol, everything.
Put cheddar on top of everything.
Switch to whole milk for everything, tea, scrambled eggs, pancakes, etc.
Think of excuses to eat double cream… scrambled eggs, mashed potato, strawberries…
Have a (whole) milk drink before bed every night (hot chocolate, horlicks, or just plain milk if that’s too processed for you).
Fatty meat cuts tend to be cheaper than lean: 20% mince instead of 5%, chicken thighs instead of breasts, pork belly, bacon, sausages…
Make yourself homemade desserts 3 or 4 times a week. A simple chocolate cake, suet putting (eg spotted dick, syrup sponge pudding etc) or pancakes if you’re pressed for time, are cheap as chips, and are dead easy to make and are over 2/3 fat and sugar.
When you eat fruit, put sugar on it.
Eat fewer vegetables as they fill you up - save space for all the fatty stuff.
You’ll pile on the pounds in no time at all.