Viroqua Food Co-op Recipe Blog

Sweet Potato Gratin with Caramelized Onions & Sage

Posted byBjorn Bergman on Wed, Sep 30, 2015 @ 03:48 PM

Sweet Potato Gratin with Caramelized Onions & Sage

Prep Time: 20 mins.
Cook Time: 55-80 mins.
Serves: 6-8
Adapted from: The Kitchn (


2 Tbsp butterSweet Potato Gratin with Caramelized Onions & Sage
2 med. onions, peeled & sliced into thin ½ moons, cut ¼" thick
3 lbs sweet potatoes (~3-4 large sw. potatoes)
Salt & pepper
4 garlic cloves, minced
¼ cp + 2 Tbsp fresh or 4 tsp + 2 tsp dried sage leaves, finely chopped
¼ tsp chipotle powder (optional)
1 cp heavy cream, milk or coconut milk
½ cp Parmesan or mild cheddar cheese, grated
Olive oil or sunflower oil


  • Preheat oven to 375°F.

  • Heat butter in wide skillet over med-heat. Once heated, add onions. Sprinkle lightly with salt. Slowly caramelize onions until nicely browned all the way through, stirring frequently, ~15-30 mins.

  • While onions caramelize, slice sweet potatoes into ¼" moons. In lightly oiled 9”x13” casserole dish, lay out one layer of potato rounds that slightly overlap. Sprinkle lightly with salt & pepper.

  • When onions are caramelized, add garlic & cook until golden. Then add fresh or dried sage, chipotle powder & cream. Mix together well making sure to scrape all caramelized brown bits off bottom of pan. Remove from heat.

  • Transfer onion & cream mixture in an even layer to casserole dish with sweet potatoes. Layer remaining potatoes on top of onion & cream layer, forming tight, slightly-overlapping rows. Sprinkle lightly with salt & pepper. It will look like there isn’t enough cream – but resist the impulse to add more. Cover casserole dish tightly with tinfoil. 

  • In preheated oven, bake casserole for 25-30 mins. or until potatoes are just tender & cream is golden brown & bubbling.

  • NOTE: baking time completely depends on how thick potatoes are cut. If potatoes are sliced thicker than ¼", increase baking time!

  • Remove from oven & remove tinfoil. Sprinkle cheese & remaining sage over top of gratin & drizzle lightly with olive or sunflower oil. Return the uncovered dish to oven for ~15-20mins. or until brown & crispy. Remove from oven & let cool for a minimum of 15mins. before slicing & serving.

Bjorn Bergman, Outreach & Education Coordinator (& Sweet Potato Lover!)

Tags: Sweet Potatoes-Yams