Drain the potatoes and allow them to cool slightly until they can be handled comfortably.

Place the potatoes on a baking sheet drizzled with olive oil and gently press each one using the bottom of a glass until flattened but still intact.

Drizzle additional olive oil over the potatoes and roast them in a hot oven until the edges turn crisp and golden brown.

Meanwhile, melt butter in a large skillet and add the sliced onions, cooking slowly until they soften and begin turning deep golden.

Stir in the minced garlic, salt, and pepper while continuing to cook the onions until they become rich, jammy, and deeply caramelized.

Add the brandy or apple juice to the onions and allow it to simmer briefly until the liquid evaporates and the flavor intensifies.

Remove the potatoes from the oven once crisp and evenly browned.

Spoon a small mound of caramelized onions onto each smashed potato.

Sprinkle shredded Gruyère cheese over the onions and return the tray to the oven until the cheese melts and becomes bubbly.

Finish by scattering chopped chives over the top and serve while hot and fragrant.