For the potato wedges: Preheat the oven to 425 degrees F.
Cut each potato in half lengthways and then cut each piece into four or five long wedges. Peel the garlic and slam it with the side of a knife to slightly crush. Toss both onto a large baking tray, drizzle a good amount of oil over and season with salt and pepper. Toss everything together and then even out into a single layer. Roast in the oven for 30 minutes.
For the burgers: Meanwhile, trim and really finely slice the spring onions (both the green and white bits), peel and finely chop the garlic and add both to a large bowl. Tip in the beef, add the breadcrumbs, mustard, ketchup and Worcestershire sauce and crack in the egg.
Slide your thumb and forefinger down the thyme sprigs to remove the leaves in one go and add those to the bowl with a good amount of salt and pepper.
Before you get your hands into the mixture, put a good drizzle of oil in a large frying pan on a high heat. Then back to the mixture and squidge it together with your hands until everything is well combined. Divide into four equal pieces, shape each into a 1-inch-thick (2.5 centimeter) patty and place on a plate.
Carefully add the burgers to the pan, reduce the heat to medium and leave to fry on the first side for 5 to 6 minutes.
As these cook, slice up the tomato and cheese (or crumble the blue cheese if using). Peel and finely slice the onion.
Give the potatoes a good toss and flip the burgers over when ready. The burgers will need about another 5 to 8 minutes, depending on how well you like them cooked.
Split the burger buns open, arrange on a baking tray and put them in the oven for a few minutes to crisp up.
Remove the buns from the oven, buttering them if you fancy. Check your burgers are cooked as you like them and place each one on a burger bun base. Layer up the tomato, cheese, onion and mustard whichever way you like and then finish with the burger bun top.
Serve with the potato wedges from the oven and a handful of arugula drizzled with some extra-virgin olive oil and balsamic vinegar. I just have to serve these with ketchup or brown sauce.