Preheat your grill to medium-high heat (about 200°C). You'll know it's ready when you hold your hand about 15cm above the grate and can only keep it there for 3-4 seconds. The grates should be clean and lightly oiled with a paper towel dipped in vegetable oil to prevent sticking.

While the grill heats, prepare the onions. In a small disposable foil tray (or a metal one you don't mind getting smoky), toss the thinly sliced onion with the olive oil and a pinch of salt. Spread them into an even layer. They will soften and caramelise as the grill works its magic.

Grill the hot dogs. Place the sausages diagonally across the grill grates, leaving a little space between each one. Let them cook undisturbed for 4-5 minutes, until the underside is deeply charred with dark brown grill marks and the casing begins to tighten. You should hear a gentle sizzle and smell a faint, smoky fragrance.

Flip the sausages and toast the buns. Using tongs, turn each hot dog over carefully. At the same time, split the buns open and place them cut-side down on the cooler edges of the grill. Cook for another 3-4 minutes. The sausages will feel firm to the touch and have visible, dark grill marks all over. The buns should be golden brown with light toasting lines and smell nutty and warm.

Check the internal temperature. Insert a meat thermometer into the centre of a sausage from the end. It should read at least 74°C for poultry sausages, or 71°C for beef. If it's not there yet, move the sausages to a cooler part of the grill for another minute or two.

Stir the onions and finish. By now, the onions in the foil tray should be soft, translucent, and tinged with brown at the edges. Give them a quick stir with a fork. Remove the buns from the grill as soon as they're toasted, then remove the sausages and the onion tray.

Assemble and serve immediately. Spread a little softened butter inside each toasted bun (this adds richness and prevents sogginess). Nestle a grilled sausage into each bun, top with a spoonful of the caramelised onions, then add ketchup, mustard, and relish to taste. Serve right away while everything is still hot and the bun is crisp.