CHASKA, Minn — Food is usually best when it goes right from the farm to the kitchen.
And that's exactly what happens at the U of M's Minnesota Landscape Arboretum. Chef Shelagh Mullen is at the helm of the Farm at the Arb program, where they plant, grow and harvest produce and herbs and then create seasonably wholesome fare.
Chef Shelagh invited the KARE 11 Saturday crew into her kitchen to whip up a Carmelized Onion and Gruyere Tart, perfect for Thanksgiving and the entire holiday season.
Here's how you make it.
Squash, Caramelized Onion and Gruyere Tart
INGREDIENTS
CRUST
- 2½ cups all-purpose flour
- 2 teaspoons sugar
- 1 teaspoon kosher salt
- 1 cup unsalted butter, cold and cut into cubes
- ½ cup + 2 tablespoons ice water
FILLING AND ASSEMBLY
- 4 tablespoons extra-virgin olive oil, divided
- 2 medium onions, very thinly sliced*
- Kosher salt
- 3 garlic cloves, thinly sliced
- 1 tablespoon Dijon mustard
- Pinch of cayenne pepper
- 4 oz. coarsely grated sharp cheddar or Gruyère
- 2 delicata squash (about 1½ lbs), halved lengthwise, seeds removed, very thinly sliced* (half moons)
- 1 small sweet potato, very thinly sliced* (half moons)
- 1 small red onion or shallot, very thinly sliced*
- 2 sprigs fresh thyme, leaves removed
- 2 tablespoons unsalted butter
- Flaky sea salt
Special Equipment:
- An 11"- or 12"-diameter fluted tart pan with removable bottom
- Mandoline or food processor (or a very sharp knife)
INSTRUCTIONS
Place a rack in the lower third of the oven; preheat to 375°.
FILLING: Swirl 2 tablespoons of oil in a large skillet to coat bottom and add the onions; season with kosher salt. Set the skillet over medium heat and cook onions, stirring occasionally and making sure to scrape the bottom of the pan, until very soft and deep golden brown, 20-30 minutes. Add garlic and cook, stirring occasionally, until onions are caramelized and deeply browned, 5-10 more minutes (if onions get super dark and stick to the pan, a few drops of water should dislodge them). Let cool.
CRUST: Place the flour, sugar, and salt in the bowl of a food processor, fitted with the metal blade. Add the cubed cold butter and pulse a few times, until the butter is evenly mixed in and resembles peas. Slowly add the water and pulse until the dough becomes crumbly and starts to stick together. Remove the dough from the food processor and put onto a clean surface. Form the dough into a ball and cover with plastic wrap. Chill the dough for at least 2 hours in the refrigerator.
Roll out dough on a lightly floured surface to about ⅛" thick. Transfer to tart pan. Lift up the edges and allow the dough to slump down into pan, don’t stretch the dough. Gently press into corners and trim excess. Freeze until firm, 15–20 minutes, or cover and chill in the fridge for up to 12 hours.
Cut sweet potato and red onion in half lengthwise, then thinly slice crosswise with mandoline or food processor. Drizzle remaining 2 tablespoons of oil over vegetables and season with kosher salt.
Brush mustard over chilled dough, then sprinkle with cayenne (from up high, but more even distribution). Layer in the cheese, then top with the caramelized onions in an even layer.
Arrange vegetables (alternating the squash, sweet potato and red onion) in concentric circles, with rounded edges facing up, starting from the outside edge, leaning slices against the crust, and working your way inward.
Loosely cover with foil and bake tart until edges of vegetables are browned (a few spots may even get deeply browned) and crust is golden brown, 60–75 minutes. Melt thyme and butter in a small saucepan and cook just until butter is bubbling. Baste the tart with the butter and thyme mixture a few times while it bakes. Sprinkle with crunchy salt, place back in the oven, uncovered for 10-15 minutes until the crust is golden brown and veggies are soft.
*Use a mandoline, a very sharp knife, or food processor, to thinly slice squash, sweet potatoes and onions.
Serves 6-8