
I do a variety of burgers with either old biddies or odds and ends from hoggets. I have tried various recipes and flavours. I add about 10% breadcrumbs made from spelt bread - 50:50 spelt and ordinary flour, not wholemeal which tastes too bready, black or white pepper and onions to all recipes. Extras added might be chillies and herbs; Herbes de Provence; tomato puree with herbs and garlic; tunisian (can't remember what I put in that but it was lovely

look for a recipe for tunisian lamb and adapt that); apricots and spices; just garlic; cranberries. For how much to use - with chillies, more than you think

. Before you go for a whole batch, add a measured proportion to a small amount of meat then cook and try it - if it's just right then add to the whole batch in the same proportions, or adjust and try again. The one flavour I don't bother with is mint - sorry daddymatty

, it just never tastes good. I've tried both dried mint and fresh mint leaves (which was wonderful while I was preparing it, with two colanderfuls of mint leaves) but the taste was lost once cooked.
Burgers shrink dramatically once cooked - I make mine about an inch thick in the largest sized pastry cutter ring I have which is about 3" across.
I have also made sausages using similar recipes, without the onion, although next time I try I will add some as it makes them juicier. We eventually decided that burgers were more versatile, as you can serve them in many different ways including with hot or spicey sauces.
You could also use some of the mince to make a true shepherds pie.