How to make a gratin dauphinois stay together?

Question

I cooked a gratin dauphinois: basically sliced potatoes covered with a mixture of cream and milk baked in an oven for about an hour.

The taste was good, the texture of the potatoes was good, but the dish did not stay together. When cutting a piece of the dish, I barely managed to move it to a plate and it kinda slid into pieces. It is as if the dish was too liquid and nothing kept the potatoes together.

When I have it at a restaurant, it is a compact dish: layers of potatoes held together that you can cut without the slices trying to escape. If you look at https://youtu.be/Gv0BroAQcG8?t=3 this is what it should like (the dish is not exactly gratin dauphinois and there is no cheese - but it is how it should look like and behave).

I did not wash the potatoes after slicing them (hoping that the starch would be enough to hold them together) but it was apparently not enough.

What can I do to "solidify" my dish?

Answer 1

Dauphinoise is one of my favorite potato dishes, I make it relatively often and I've never had a problem with it coming apart, so I'll go through my method and point out potential trouble points along the way. I usually serve them straight out of the oven after a 10 minute rest without issues. I've also made them ahead of time and reheated them in the oven which also works well.

1. Starchy potatoes: Potato slices will stick together if they have enough loose starch and moisture to form a sticky film which acts as a glue. If your potatoes are too wet or dry you won't get this, I use a medium potato and get very good results, so use an all-rounder potato variety
2. Thin slices: I use a food processor to slice the potatoes thinly, not the thinnest blade but the next to thinnest blade. Thin slices hold together better, I expect because there's much more surface area overall to stick. So, nice thin slices will work better. This can take forever by hand, a mechanical solution helps enormously. If you don't have a food processor maybe get a mandolin, just make very sure to be careful as they can be dangerous
3. Overlapping: When I lay the potatoes out I take a stack of slices potatoes and spread that stack out like a deck of cards on the bottom of the dish. The potato slices should be sticking together well already at this point, the goal is to keep them together. I keep adding stacks this way, spreading them around so I get coverage while overlapping them to make sure they interlock. I use small end pieces to fill in any gaps. You want a solid mass of potato slices
4. Press them down: As I lay the potato slices I push down every few layers to make sure they stick well, this also helps to detect empty spots so you can fill them. I don't put weights on the top, but before I pour the cream over I press down on top with my palms for a few seconds
5. Pour the hot liquid in last: the idea is to have a solid mass of potato slices which you pour the hot liquid around. Don't worry about the liquid getting where it needs to go, it will run in through cracks and gaps, you don't want to disturb your layering
6. Bake until they are well done: you want a skewer to go in like it's butter, at least once it's through the top crust
7. Rest the potatoes: give them 10 minutes after you take them out before serving, then use a good sharp knife to cut

Answer 2

A few suggestions:

• Before the final cooking in the oven (in the method I use, the sliced potatoes are first boiled with cream and milk before being assembled in the dish), place in the fridge with a weight on top to compress the potatoes a little.

• Cook (perhaps leave off any cheese you'd put on top) fully, store overnight and reheat to serve.

• Perhaps reduce the liquid a little, either by using less to begin with or by boiling for longer to thicken it (the starch from the potatoes helps here too).

• When you cut it to serve, use a sharp knife and try to avoid pushing on the potatoes either laterally or downwards, as both can cause them to slide out of formation.

Regarding the video you linked, notice that they are giving themselves a few advantages: each individual gratin is composed of individual slices of the same size stacked (rather than having multiple pieces of potato in each layer) so it cannot come apart horizontally before cutting, they are careful to use the fork to keep it together and there is cheese in the middle which melts onto the outside providing structural support.

On the whole, even when I've seen professional dauphinoise portions that look beautiful and neat as served, they come apart once the diner starts cutting into them (unless the diner is very careful), so be aware that your expectations might be higher than is needed.