Two pounds of thinly sliced Yukon Golds and four cups of broccoli layered under a sauce of oat milk thickened with cornstarch and made savoury with a third of a cup of nutritional yeast.
Thirty minutes covered, then a gluten-free crumb topping tossed in olive oil for a final twelve to fifteen minutes uncovered.
Why This Recipe Works
- The potatoes are parboiled for five minutes first. Thin slices in a covered dish would still be firm at thirty minutes, and the uncovered stage is short because it belongs to the topping rather than to the vegetables.
- Cornstarch is whisked into cold oat milk before it meets heat. This is the one non-negotiable technique in the recipe — cornstarch tipped into a warm pan clumps instantly and cannot be whisked smooth.
- The sauce is simmered only until lightly thickened. It thickens further in the oven, and a sauce brought to full thickness on the hob turns solid under thirty covered minutes.
- Foil for the first thirty minutes and off for the last twelve to fifteen. The covered stage steams the vegetables tender; the uncovered stage is the only chance the crumbs get to crisp.
- Yukon Golds rather than a floury potato. They hold their slices in a sauced casserole where a russet would break down into the sauce entirely.
What Each Vegan Ingredient Replaces
This is a dairy casserole rebuilt without dairy, and every substitution is doing one specific job rather than approximating cheese in general. Knowing which is which is what stops a swap going wrong.
| In the recipe | Usually | Here | Why it matters |
|---|---|---|---|
| The savoury, cheesy note | Cheddar or a cheese sauce | 1/3 cup nutritional yeast | It brings the glutamate depth that reads as cheese. A third of a cup is a lot by volume and it needs to be — halve it and the sauce tastes of oat milk. |
| The body of the sauce | A butter-and-flour roux | 3 tablespoons cornstarch whisked into 2 cups oat milk | Cornstarch thickens without gluten and without the raw-flour stage. It is whisked into the cold milk first, which is the only way it disperses. |
| The dairy liquid | Whole milk or cream | 2 cups unsweetened plain oat milk | Oat milk is the neutral one. Sweetened or vanilla versions are unusable here, and nut milks can split when simmered with acid. |
| The sharpness | Sour cream or a sharp cheese | 1 teaspoon Dijon mustard | A single teaspoon cuts the richness. If the page is to claim gluten-free, this is one of the two packaged items that must be certified. |
| The fat that carries the aromatics | Butter | 2 tablespoons vegan butter or olive oil | Either works. The garlic gets thirty seconds in it before the milk arrives, which is what stops it tasting raw in the finished sauce. |
| The crisp top | Buttered breadcrumbs or a cheese crust | 1/2 cup gluten-free breadcrumbs with 1 tablespoon olive oil | The oil is what lets crumbs brown in twelve to fifteen minutes. This is the second packaged item that must be certified for a gluten-free claim. |
Ingredient Notes
- Unsweetened plain oat milk
- Two cups, and both words matter. Sweetened or flavoured plant milks are unusable in a savoury sauce, and oat is the neutral one that will not split.
- Nutritional yeast
- A third of a cup. This is the savoury backbone of the dish rather than a garnish, and reducing it leaves the sauce tasting of thickened oat milk.
- Cornstarch
- Three tablespoons, whisked into the cold milk with everything else at step 3. Never added to a hot pan.
- Gluten-free breadcrumbs and Dijon
- These are the two packaged items that decide whether the gluten-free claim holds. Both must be certified gluten-free — Dijon in particular varies by brand.
- Yukon Gold potatoes, thinly sliced
- Two pounds, sliced thin and evenly. Thickness variation is the main reason a slice or two stays firm when the rest are tender.
How to Make It
Heat the oven
Heat the oven to 375°F and lightly grease a 9 x 13-inch baking dish.
Parboil the potatoes
Steam or parboil the potato slices for 5 minutes; drain well.
Whisk the sauce base cold
Whisk the oat milk, cornstarch, nutritional yeast, Dijon, onion powder, salt and pepper.
Cook the garlic and thicken
Melt the vegan butter in a saucepan, cook the garlic for 30 seconds, then whisk in the oat-milk mixture. Simmer until lightly thickened.
Layer and sauce
Layer the potatoes and broccoli in the baking dish and pour the sauce evenly over them.
Bake covered
Cover with foil and bake for 30 minutes.
Add the topping
Mix the gluten-free breadcrumbs with olive oil, uncover the casserole and scatter them over the top.
Bake uncovered
Bake for another 12 to 15 minutes, until the potatoes are tender and the top is crisp.
Success Tips
- Slice the potatoes to an even thickness — a mandoline earns its place here.
- Whisk the cornstarch into the cold oat milk, never into the hot pan.
- Stop the sauce at lightly thickened; the oven finishes it.
- Drain the parboiled slices properly before they go into the dish.
- Keep the last tablespoon of olive oil back for the breadcrumbs.
Serving Ideas
A green salad or a simple bean dish alongside. It is rich and starchy on its own, so what it wants is something sharp rather than another baked side.
Storage and Reheating
Refrigerate
Refrigerate in an airtight container for up to 4 days. The crumb topping softens overnight and partly re-crisps in the oven.
Freeze
Freeze cooled portions for up to 2 months, ideally without the topping. Cornstarch-thickened sauces can weep slightly on thawing and come back together with gentle heat.
Reheat
Reheat uncovered at 350°F for 20 minutes so the top re-crisps. Covered reheating leaves the crumbs soft.
Frequently Asked Questions
The sauce went lumpy.
The cornstarch met heat before it met cold liquid. It has to be whisked into the oat milk at step 3, off the heat, and only then poured into the pan.
Is this genuinely gluten-free?
Only if the packaged ingredients are. The breadcrumbs and the Dijon are the two that vary by brand, and both need to be certified gluten-free for the claim to hold.
Can I use almond or soy milk?
Oat is what this sauce is written for. Others will thicken, but soy can taste beany against nutritional yeast and some nut milks split when simmered with mustard.
Do I have to parboil the potatoes?
Yes. Five minutes is what lets thin slices finish tender inside a thirty-minute covered bake — the uncovered stage is too short to make up the difference.
