Preheat the oven to 400°F. Lightly spray a standard 12-cup muffin tin with cooking spray.

Melt the butter in a skillet over medium-low heat. Add the sliced onions and a pinch of salt. Cook, stirring occasionally, for 15–20 minutes, or until golden brown and sweet. Set aside.

Peel and clean the potatoes, then slice them into thin, even rounds.

In a small bowl, combine the smoked paprika, dried thyme, cayenne pepper if using, lemon zest, salt, and black pepper.

Assemble the potato stacks by placing 2 potato slices in each muffin cup. Sprinkle with a pinch of the seasoning blend.

Add a small amount of grated Gruyere and a few caramelized onions.

Repeat the layers of potatoes, seasoning, cheese, and onions until each muffin cup is full.

Pour about 1 tablespoon of heavy cream over each stack.

Bake for 30–35 minutes, or until the tops are golden brown and the potatoes are tender when pierced with a knife.

Let cool slightly. Run a knife around the edges and gently lift each stack out of the muffin tin. Serve warm.