Carefully remove the potatoes from the microwave (they'll be hot!), discard the paper towels, and let cool slightly before handling. Meanwhile, preheat the air fryer to 400°F.

Pierce each potato a few times with a fork, then rub generously with olive oil and season all over with salt and pepper.

While the potatoes cook, begin caramelizing the onions. Melt 3 tbsp of butter in a large skillet over medium heat. Add the sliced onions and a generous pinch of salt, stirring to coat. Cover with a lid and let the onions steam for 5-10 minutes, stirring occasionally, until softened and beginning to release their moisture.

Remove the lid, reduce the heat to medium-low, and continue cooking for 25-30 minutes, stirring occasionally, until deeply caramelized and golden brown. If the bottom of the skillet starts to get too dark, reduce the heat slightly.

Add a splash of dry white wine to deglaze the pan, scraping up any browned bits from the bottom. Cook for another 1-2 minutes, until most of the liquid has reduced. Remove from the heat and stir in a few dashes of Worcestershire sauce.

Cut a cross into the top of each potato, being careful not to slice all the way through. Gently press down and pull apart to open up the potatoes.

Add ½ tbsp of the remaining butter to each potato and let it melt, then use a fork to lightly mash it in. Use extra butter here if you like. Next add a spoonful of crème fraîche to each potato and gently mash again until creamy, being careful not to tear the skins too much.

Spoon a generous amount of caramelized onions over each potato and finish with plenty of freshly grated Gruyère.

Finish with fresh thyme leaves and a little freshly cracked black pepper, if you'd like. Serve while hot!