Harvest Fennel Potato Casserole (Easy Thanksgiving Side)

If you are like me and try to pre-cook a few side dishes before a big family or friends gathering, then this fennel potato casserole is one you will want to make two of every Thanksgiving. This is the one dish my family and friends hover over before the turkey even gets time to rest post-cooking. I had a small mountain of fennel bulbs and (not surprisingly for November) enough potatoes to re-tile the kitchen counters. Add a few late-season carrots, an onion, and a fistful of peppery arugula, and suddenly you’ve got a cozy casserole that makes the whole house smell delish.

It’s simple, earthy, and quietly elegant — the sort of thing you slide onto the table and watch disappear spoonful by spoonful. And if you grow fennel (or panic-buy it at the farmers market the way I sometimes do), this is a mighty tasty way to use it up.

Why This Recipe Works

A warm, wholesome side dish built from sturdy fall vegetables. Great for all the fall holidays, especially Thanksgiving! If you love breakfast, this can be a super unique change of pace by adding an over easy egg to it.

Fennel, potatoes, onions, and carrots show up reliably in fall — but this casserole happily welcomes whatever root veggies you’ve piled up from the garden.

Seasonal Flexibility

Healthy & Wholesome

A mix of roasted vegetables bound by a light cream sauce. Nothing heavy — just cozy.

Simple Method

Roast the veggies, make a quick stovetop sauce, toss it all together, and bake. That’s it.

For something more complex, use your pellet smoker of choice (Traeger, Pit Boss, Weber, or similar) and get those veggies smoky!

Make-Ahead Friendly

Assemble earlier in the day and bake before the feast. Leftovers? Even better the next day or freeze and eat for a month.

Ingredients

• 2 medium fennel bulbs, cored and sliced
• 3 cups potatoes, diced (Yukon Gold or similar)
• 2 large carrots, sliced
• 1 large onion, chopped
• 2 cups fresh arugula
• 3 tablespoons olive oil
• 2 teaspoon salt (more to taste)
• 1 teaspoon black pepper
• 1 cup vegetable broth
• 1 cup milk or half-and-half
• 2 tablespoons butter
• 2 tablespoons flour
• ½ cup grated Parmesan (optional but wonderful)
• Pinch of nutmeg (trust me on this)

(Sub notes: swap half of the potatoes with sweet potatoes, or use kale instead of arugula if that’s what the garden gave you.)

Yield & Servings

Makes one 9×13 casserole dish — about 6–8 hearty side servings, depending on how many cousins show up hungry.

Fresh Produce

Fennel brings sweetness and a hint of anise; carrots round out the earthiness; arugula adds a peppery lift at the end.

Proteins or Grains

Not much here — it’s a veg-forward side. You can stir in cooked farro or quinoa for a heartier casserole.

Flavor Boosters

Parmesan, nutmeg, roasted edges on the veggies, and that peppery arugula.

Instructions

1. Preheat oven to 400°F.
2. Toss fennel, potatoes, carrots, and onion with olive oil, salt, and pepper. Spread on a baking sheet.
3. Roast for 25–30 minutes, until they get those little caramelized edges that make life better.
4. While veggies roast, melt butter in a saucepan. Whisk in flour to make a quick roux.
5. Add broth and milk slowly, whisking until smooth. Cook 3–4 minutes until thickened.
6. Stir in Parmesan and a pinch of nutmeg. Taste and adjust seasoning.
7. Transfer roasted veggies to a casserole dish. Fold in the arugula so it wilts a bit.
8. Pour the sauce over everything, give it a gentle toss, and bake at 375°F for 20 minutes, until bubbling and golden at the edges.

Cooking Variations

Stovetop Method

Skip the final bake — simmer roasted veggies in the sauce for 5–7 minutes.

Oven/Grill Method

Bake, covered, for 15 minutes, then uncover to brown. Works great on a grill or a smoker as mentioned above, with indirect heat.

Slow Cooker / Instant Pot

Roast the veggies first (don’t skip!), then warm everything together on low for 1–2 hours.

Easy Substitutions & Seasonal Variations

A little flexibility makes this dish a year-round keeper.

Vegetables or Greens

• Swap arugula for spinach, kale, or chard.
• Add cubed squash or parsnips.

Proteins

• Fold in leftover shredded turkey for a post-Thanksgiving version.
• Add white beans for a vegetarian protein bump.

Grains or Starches

• Stir in cooked farro, barley, or leftover rice.

Spring Version

Use young fennel, baby potatoes, and fresh spinach.

Summer Version

Roast the zucchini with the onions and add fresh basil at the end.

Fall Version

Lean into roots — add parsnips, rutabaga, or diced squash.

Winter Version

Use stored potatoes and onions with frozen greens.

Serving Suggestions & Storage

This casserole plays nicely with turkey, roasted chicken, or even a simple grain bowl the next day.

Pairings

Serve alongside roasted turkey, grilled sausages, or mushroom gravy.

Toppings or Garnishes

A squeeze of lemon, toasted breadcrumbs, chopped fennel fronds, or extra Parmesan.

Fridge

Keeps 3–4 days in an airtight container.

Freezer

Freeze up to 2 months. Thaw and reheat covered to keep it creamy.

Frequently Asked Questions

Can I freeze this recipe?

Yes — it freezes beautifully after baking.

How long does it last in the fridge?

About 3–4 days.

Can I make this vegetarian/vegan/gluten-free?

• Vegetarian: Already is.
• Vegan: Use olive oil instead of butter, plant milk, and skip Parmesan or use a vegan one.
• Gluten-free: Use cornstarch instead of flour.

What seasonal produce works best?

Any fall roots — potatoes, carrots, fennel, onions, squash, parsnips, or even sunchokes.

Final Tip / Closing

If you’ve got a mix of garden vegetables rolling around this time of year, don’t overthink it — toss them in, roast them well, and let this casserole carry the day. And if your fennel bulbs are a little lopsided or your potatoes still wear a bit of soil? Give those taters a little more scrub and accept the fennel with all its imperfections. That’s real food, and it tastes like home.