We can thank the French for a lot of wonderful culinary things – the baguette, steak frites, vin chaud, French onion soup, alllll the fromage, croissants, the list goes on and on. And somewhere up on that list is the gratin.
Anything gratinée, or au gratin is really just something that’s been finished with some sort of cheesy or breadcrumby topping that gets brown and bubbly and crispy when broiled in the oven. So this cheesy, gooey root vegetable gratin certainly falls in that category.
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Why make a gratin?
There are a few dishes I think every home cook should have in their back pocket, and a gratin is one of them. Why?
- It’s versatile – make with almost any vegetable, pasta, rice, etc.
- It’s hands off – after you assemble the gratin, all the cooking happens in the oven with little oversight required
- It’s a crowd pleaser – as a general rule, people like melty, bubbly cheese baked into things
A gratin is also a great way to use up vegetables you might have in your fridge. I have a big bag of both broccoli and cauliflower florets in my fridge as we speak that I’ll probably make into a broccoli and cauliflower gruyere gratin at some point in the coming days.
I’m pretty partial to vegetable gratins, though potatoes are certainly very classic. Vegetables balance the richness of the cream and cheese in the gratin, and they bake up so nicely in the oven.
#1 Rule for Making a Successful Gratin
The number one rule for making a successful gratin is to make sure you use ingredients that require the same amount of cooking time. OR cut your ingredients in a way that ensures they have the same amount of cooking time.
For example, for this root vegetable gratin I used a variety of different tubers: fingerling sweet potatoes, hakurei and regular turnips, celery root, and sunchokes. The hakurei turnips, sunchokes, and fingerling sweet potatoes were much smaller than the regular turnip and celery root.
The vegetables I used were almost all sourced from my favorite farmers’ market, so they’re pretty specific. Feel free to substitute for whatever root vegetables you can find.
To combat the size difference, I cut the turnip and the celery root into quarters. Then when I sliced the vegetables, I sliced the sunchokes, hakurei turnips, and fingerling sweet potatoes thicker than I sliced the turnip and celery root.
This meant that when the gratin cooked, all the vegetables were about the same level of tenderness when they were done.
How to Prepare a Root Vegetable Gratin
The first step in the process of making your root vegetable gratin is to slice the vegetables. I used my mandoline for this, and guys it’s a life saver. It ensured all the slices were consistent and made super quick work of the whole thing.
Then you season the vegetables BEFORE you layer them in your baking dish. So the vegetables all get coated with the cream, salt & pepper, and cheese prior to layering.
#2 Rule for Making a Successful Gratin
Make sure you season the vegetables liberally! Especially using root vegetables which have a lot of natural sweetness when cooked, you need to add a lot more salt than you think.
In addition to the salt, I used blue cheese to amp up the flavor. For any blue cheese haters out there, just trust me on this one. When cooked into the root vegetable gratin, the sharpness of the blue cheese that some people dislike fades away. You’re left with just some extra punches of savory that kick it up a notch.
Layering a Gratin
I love to make a gratin with lots of pretty layers. For this root vegetable gratin it went like this:
- Layer of turnip and celery root –> extra parmesan –> fresh thyme
- Layer of sweet potatoes, hakurei turnips and sunchokes –> blue cheese –> extra parmesan –> fresh thyme
- Last layer of turnip and celery root –> extra parmesan –> fresh thyme
- Final layer of sweet potatoes, hakurei turnips and sunchokes –> blue cheese –> extra parmesan –> cracked black pepper
Then you bake the whole thing in the oven, covered at first to steam the vegetables evenly, then uncovered to get that top layer of cheese browned to gratin perfection.
Serving Root Vegetable Gratin
This gratin is special enough as a side for a nice dinner, but it also plays great with a nice green salad for a weeknight meal.
I like to have some fresh thyme and sea salt for each person to garnish their gratin slices with a little extra seasoning if they want. This is a simple dish, but one that is pure comfort food.
Root Vegetable Gratin
A cheesy winter root vegetable gratin with fresh thyme is comfort food at its finest!
- 6 fingerling sweet potatoes or 1 large sweet potato
- ½ lb celery root peeled and quartered
- 1 large turnip quartered
- 1 pint sunchokes rinsed and scrubbed
- 1 bunch hakurei turnips leaves and root end removed
- 1 pint heavy cream
- 2 cups grated parmesan cheese divided
- 2 ½ tsp kosher salt
- 1 tsp black pepper divided
- ⅓ cup crumbled blue cheese divided
- 2 tsp thyme leaves divided
Preheat the oven to 400
Begin by cleaning and slicing the vegetables. The smaller vegetables should be cut slightly thicker than the larger vegetables. You should have 6-8 cups of sliced vegetables in total
Combine the vegetables with all of the cream, half of the parmesan, all of the kosher salt, and half of the black pepper in a large mixing bowl. Coat all the vegetables with the seasoning
Grease a medium au gratin dish (or an 8×8 baking dish). Add a layer of vegetables, plus 1/4 cup parmesan cheese, plus 1/2 tsp fresh thyme
Add a second layer of vegetables plus half the blue cheese, plus 1/4 cup parmesan cheese, plus 1/2 tsp fresh thyme
Add a third layer of vegetables plus 1/4 cup parmesan cheese, plus 1/2 tsp fresh thyme
Add a 4th layer of vegetables and any remaining cream and cheese in the mixing blow plus the remaining blue cheese, parmesan cheese, and thyme. Finish with fresh cracked black pepper.
Cover with foil and bake 40 minutes or until the vegetables are almost fork tender
Remove the foil and bake uncovered for 20-25 minutes or until the cheese is browned and the vegetables are fork tender