Caramelized Onion Tart

There is nothing like the taste of a nicely caramelized onion – deep, earthy, sweet and savory jam. But caramelizing onions is a time consuming labor of love well worth the effort, most of the time.

Lucky for those of us with pressure cookers, the geniuses in the labs of Modernist Cuisine came up with a brilliant hack to get those delicious browned onions cooked and ready to eat in half the time and with virtually no need for our attention once the lid is locked! This is seriously one of our favorite shortcuts to one of those foods we associate with very long, closely tended cooking times.

We put a batch of pressure cooker caramelized onions to use in an onion tart intended for a holiday brunch party. But we ended up eating the whole thing ourselves over the course of several days. No complaints here!

Any savory pie crust recipe will do. We’re partial to America’s Test Kitchen’s tart crust recipe. As for the custard filling, we adapted this one from Monday Morning Cooking Club: The Feast Goes On (recipe published on

Caramelized Onion Tart

Pressure-Caramelized Onions

(From Modernist Cuisine At Home)

  • 4 3/4 cups (500 g) yellow onion, sliced thin
  • 1/4 teaspoon (1.5 g) baking soda
  • 3 tablespoons (35 g) unsalted butter, cubed
  • Salt, pepper and sugar to taste

Combine sliced onions and baking soda in a large bowl, mixing thoroughly. Divide the onion mixture evenly into three 500 ml/16 oz. canning jars. Divide the butter evenly among the filled gars. Tighten the lids fully, and then unscrew them one-quarter turn so that the jars don’t explode.

Place the filled jars on a rack or trivet in the base of a pressure cooker, and add 1 inch of water. Pressure-cook at a gauge pressure of 1 bar/15 psi for 40 minutes. Start timing as soon as full pressure has been reached. Let the cooker cool, or run tepid water over the rim, to de pressurize it. Let the jar contents cool before opening to avoid splattering.

Transfer the cooked onions to a pot. Simmer over medium heat, stirring occasionally, until the liquid has reduced to a syrup, 10-12 minutes.

Season the onions to taste, and set aside.


(from The Cook’s Illustrated Cookbook)

  • 1 1/4 cups all-purpose flour
  • 1 tablespoon sugar
  • 1/2 teaspoon salt
  • 8 tablespoons unsalted butter, cut into 1/2-inch cubes and chilled
  • 2-3 tablespoons ice water

Spray 9-inch tart pan with vegetable oil spray. Pulse flour, sugar, and salt in food processor until combined, about 4 pulses. Scatter butter pieces over flour mixture; pulse until mixture resembles course sand, about 15 pulses. Add 2 tablespoons ice water and process until large clumps form and no powdery bits remain, about 5 seconds, adding up to 1 tablespoon more water if dough will not form clumps. Transfer dough to prepared tart pan; pat dough into pan. Lay plastic wrap over dough and smooth out any bumps or shallow areas. Place tart shell on plate and freeze for 30 minutes.

Adjust over rack to middle position and heat oven to 375 degrees. Place frozen tart shell on baking sheet. Spray piece of extra-wide Healey-duty aluminum foil with vegetable oil spray and gently press against dough and over edges of tart pan. Fill with pie weights and bake until top edge just starts to color and surface of dough no longer looks wet, about 30 minutes. Remove from oven and remove foil and weights. Return baking sheet with tart shell to oven and bake until golden brown, 5-10 minutes. et baking sheet with tart shell on wire rack to cool while preparing the filling.

Custard Filling

  • 1 cup heavy cream
  • 4 large egg yolks
  • freshly grated nutmeg
  • Salt and pepper to taste

In a bowl, gently beat egg yolks into into cream until well incorporated. Add caramelized onions and freshly grated nutmeg. Mix well to evenly distribute onions throughout custard. Pour into prepared tart shell and bake in a 350 degree oven until center of custard is set, approximately 40-45 minutes.

Remove tart from oven and let cool on a rack for 10 minutes. Remove rim of tart pan and carefully slide a spatula between tart pan bottom and tart to loosen it. Slide tart onto serving plate, slice and serve!


  • Add fresh thyme leaves to custard filling before baking
  • Sprinkle blue cheese crumbles over cooke tart and warm just to melt cheese
  • Add bacon crumbles to custard filling before baking
  • Use half-n-half in place of heavy cream for a slightly lighter tart

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