Preheat your oven to 425°F. While the oven heats, wash the potatoes thoroughly under cold water and pat them dry completely—this helps them crisp up during roasting. Place each potato on a cutting board and carefully slice it about three-quarters of the way through at roughly ¼-inch intervals, being careful not to cut all the way to the bottom. The potato should stay intact so the slices fan out but stay connected. Stand each sliced potato upright on a rimmed baking sheet, then gently fan out the slices slightly to create a beautiful presentation and expose more surface area for the toppings.

Combine the melted butter and olive oil in a small bowl. Brush this mixture generously all over the fanned potatoes, making sure to get into the slices as much as possible—this ensures even browning and helps the potatoes crisp up. Sprinkle the salt and freshly ground black pepper evenly over all the potatoes. Roast in the preheated oven for 45–60 minutes, until the potatoes are completely tender when pierced with a fork and the exposed edges are golden and crispy. I like to check them around the 45-minute mark to gauge how they're browning—every oven is different!

Remove the roasted potatoes from the oven and while they're still hot, carefully distribute the shredded sharp cheddar cheese between the slices of each potato, working down into the gaps. The residual heat will start melting the cheese. Sprinkle the crumbled bacon and chopped green onions evenly over the tops of all four potatoes. Return the baking sheet to the oven for 5–10 minutes, just until the cheese is fully melted and bubbly. I find that the bacon gets slightly crisper during this final roast, which adds great texture to the final dish.

Transfer the loaded hasselback potatoes to serving plates and serve immediately while the cheese is still melted and everything is warm. Dollop each potato generously with sour cream on top—or serve it on the side so guests can add as much as they'd like. The cool, tangy sour cream is the perfect complement to the rich, cheesy, crispy potatoes.