In a nutshell - fats and proteins. You need to add in fats where possible, as they are twice as energy-dense as protein sources (gram for gram...)
Don't trim the fat off meat, buy grain-fed beef with lots of marbling (and flavour!). Add a knob of homemade herb butter on your veges...
If you are eating dairy: Try Gippsland Dairy (full fat) yoghurt - they have fruit flavours , and most - but NOT ALL have no added crap (aka: starchy thickeners and other nasties)!

it's sweetend with sugar, so it's not like Greek Yoghurt . Drink full cream milk.....
Get baking!
