Caramelized Shallot Fontina Potato Gratin Step-by-step instructions

Before you start

Before starting, make sure the caramelized shallots are ready – they can be made up to 3 days ahead and stored in the refrigerator. Thinly slice the potatoes using a mandoline or a sharp chef's knife; aim for uniform 1/8-inch slices so they cook evenly.

Shred the Fontina if you bought it in a block, and chop the fresh rosemary. Have all ingredients measured and within reach before you begin layering.

Instructions

Layer and Pour

1. 1Prep the Slow Cooker
   Lightly coat the insert of a 6-quart slow cooker with nonstick spray or a thin layer of butter. This helps the gratin release cleanly and prevents sticking.
   Look for The insert is lightly coated and ready.
   Tip Use a ceramic or nonstick insert for the best release.
2. 2Layer the Potatoes
   Arrange one-third of the sliced red potatoes evenly in the bottom of the slow cooker. Sprinkle with a pinch of salt and pepper.
   Look for Potatoes cover the bottom in an even layer.
   Tip Slice potatoes about 1/8-inch thick for even cooking.
3. 3Add Shallots and Cheese
   Scatter one-third of the caramelized shallots over the potatoes, then sprinkle with one-third of the shredded Fontina and a little chopped rosemary.
   Look for The layer is dotted with shallots and cheese.
   Tip Reserve some rosemary for the top if desired.
4. 4Repeat Layers
   Repeat the layering process two more times, finishing with a final layer of potatoes, then the remaining shallots, Fontina, and rosemary.
   Look for All layers are in place, with cheese and shallots on top.
   Tip Press down gently on the layers to compact them.
5. 5Pour Cream Over
   Pour the heavy cream evenly over the top, allowing it to seep down between the layers. Season with any remaining salt and pepper.
   Look for The cream pools at the edges and the top looks glossy.
   Tip Use a spatula to gently press down so the cream coats the potatoes.

By the end of this phase, the slow cooker is filled with alternating layers of potatoes, caramelized shallots, Fontina, and rosemary. The heavy cream has been poured over the top and is beginning to seep down between the layers. The surface looks glossy and inviting, with the cheese peeking through the cream. The layers are compact and even, ready for the slow cooking process to begin.

Slow Cook Until Bubbly

6. 6Cook on Low
   Cover the slow cooker and cook on LOW for 4 1/2 hours, until the potatoes are tender when pierced with a fork and the cheese is bubbly and golden around the edges.
   Look for The gratin is bubbling at the edges and the cheese is melted.
   Tip Avoid lifting the lid during cooking to keep the heat steady.
7. 7Check for Tenderness
   After 4 1/2 hours, insert a fork into the center of the gratin. The potatoes should be completely tender with no resistance. If not, continue cooking in 15-minute increments.
   Look for A fork slides in easily and the potatoes are soft.
   Tip If the top is browning too fast, you can turn the slow cooker to WARM for the last 30 minutes.

After 4 1/2 hours on LOW, the gratin is bubbling at the edges and the cheese has melted into a golden blanket. The kitchen smells of roasted shallots, rosemary, and creamy cheese. A fork inserted into the center meets no resistance, and the potatoes are tender and creamy. The sauce has thickened and coats the layers, creating a cohesive dish that is almost ready to serve.

Rest and Serve

8. 8Rest the Gratin
   Turn off the slow cooker and let the gratin rest, uncovered, for 10 minutes. This allows the sauce to set slightly and makes it easier to slice.
   Look for The gratin is slightly firm and no longer bubbling.
   Tip Resting helps the layers hold together when serving.
9. 9Garnish and Serve
   Slice the gratin into squares or wedges directly from the slow cooker. Top each serving with crispy fried shallots and a few fresh rosemary needles.
   Look for The gratin is golden, creamy, and garnished with crispy shallots.
   Tip Use a wide spatula to lift out clean portions.

After resting for 10 minutes, the gratin has set slightly and is easier to slice. The top is golden and slightly crispy in spots, while the interior is creamy and steaming.

Garnished with crispy fried shallots and fresh rosemary, each serving is a beautiful square of layered potatoes, cheese, and shallots. The texture is luxurious – creamy, tender, and rich with a satisfying contrast from the crispy topping.

Common mistakes

One common mistake is lifting the lid to check on the gratin too often, which lets out heat and extends the cooking time. Another is slicing the potatoes too thick, which leads to undercooked centers.

Use a mandoline for consistent slices. Also, avoid using low-fat cream or milk – they can separate or produce a thin sauce. Finally, don't skip the resting time; it allows the gratin to firm up and makes serving much easier.

How to tell it’s done

The gratin is done when the potatoes are completely tender when pierced with a fork – there should be no resistance. The cheese should be fully melted and bubbly, with a golden-brown crust around the edges. The cream should be absorbed and thickened into a creamy sauce, not watery.

If the top is browning too quickly but the potatoes are still firm, reduce the heat to WARM and continue cooking until tender. Let the gratin rest for 10 minutes before serving so it sets and slices cleanly.