We’re playing around with another viral food trend in this post – the TikTok upside down puff pastry hack. My version here takes things to a decidedly savory place, a’ la French Onion Soup. This Upside Down French Onion Soup is one of the best things I’ve made in a while (pats self on back) and it utilizes this upside down puff pastry hack to achieve a golden brown, cheesy crust and a perfectly cooked bottom. We’ll whip up a French Onion Soup concentrate (this is what I’m calling it) and shower everything with lots of Gruyere cheese for a puffy hand-held version of this soup that you guys are going to just LOVE.

Table of Contents

Okay, so what is French Onion Soup concentrate?

For this recipe, we’re going to create what I’m calling “French Onion Soup Concentrate.” This is essentially a massive heap of very thinly sliced onions that we’ll cook down and flavor intensely with the things that make french onion soup so tasty. But rather than using beef stock, we’re using stock concentrate. This helps us nail the flavor of a classic French Onion Soup without having all the liquid (as that would really ruin the tart, you know?)

While I tend to stay away from single-use kitchen tools, I do love a mandoline. That’s what helps me achieve paper-thin slices of onion that cook quickly and evenly for this tart. You can purchase mandolines easily (mine’s from Target) and they’re not expensive at all (I mean, you can get an expensive one, but you certainly don’t have to).

Flavor Variations for this Hand-Held French Onion Soup

Adding some thinly sliced apples to this is so lovely, especially is you make it in the fall. Same goes for pears. Using a variety of onions could help deepen the flavor, creating interest (sweet onions, red onions, and shallots would be nice).

Changing up the kind of cheese you ouse is fine as well, as Gruyere is a little pricier. So, I’d suggest a white cheddar or a Swiss as a solid replacement, if you like.

What You’ll Need to Make This Hand-Held French Onion Soup

This is one of those recipes where we could say that the biggest ingredients is TIME. It just takes time to slice all of those onions and then about 12-ish minutes to get them tender like we want them (they’ll cook even more in the oven). While you could absolutely do this with a cutting board and chef’s knife, I really do suggest using a mandoline to get them paper thin. When the onions are sliced that thinly, they cook down into almost an onion soup jam of sorts and are just lovely. Also, the mandoline helps prevent your eyes from watering quite so much. We love this.

INGREDIENTS

3 tablespoons olive oil, plus more as needed

2 pounds onions very thinly sliced (see note about mandoline)

3 teaspoons beef stock concentrate (such as Better Than Bouillon)

2 teaspoons Worcestershire sauce, plus more as needed

2 teaspoons dried Italian seasoning

1 teaspoon garlic powder

1 to 2 teaspoons fresh thyme leaves

Salt and pepper

1 sheet puff pastry, thawed

8 ounces Gruyere cheese, shredded

Serving suggestions: I like to pile up a simple salad of fresh arugula dressed lightly with lemon juice and olive oil.

How to Make our Upside Down French Onion Soup

This is a very simple preparation, all told, and goes a little something like … slice a heap of onions, cook them down with some very French Onion soupy things, pile them onto yet another heap of amazing cheese, cover in a puff pastry blanket, and then put it down for a nice oven nap until crunchy and golden and soon-to-be ICONIC.

DIRECTIONS

Preheat the oven to 400 degrees F. Adjust the oven rack to the middle position. Cover a large baking sheet with parchment paper.

Add the oil to a large skillet over medium heat, along with the onions. Cook for about 5 minutes, or until soft and relatively tender (this goes fast if they’re sliced extra thin).

Add the stock concentrate, Worcestershire sauce, Italian seasoning, and garlic powder. Cook for 6 to 8 minutes more, stirring really well to get all the flavors evenly distributed. Taste, and season with salt and pepper. Add the thyme .

Sprinkle the grated Gruyere on the parchment paper, in an even layer that will fit nicely under the puff pastry (no larger than that). Top with the onion mixture, using about a heaping cup or so – you’ll likely have enough left over to make a second tart (see note).

Lay the pastry over top, fully covering the filling. Using the tips of a fork’s tines, press all around the edges of the pastry, creating a seal and simple design. Bake until very golden brown and cooked through about 30 to 35 minutes. Cool for at least 10 minutes before gently running a knife under the tart and flipping over onto either a large plate, platter or another baking sheet. Top with a simple arugula salad, if you like, and enjoy warm.

NOTES:

Note 1: I usually snag a 3-pound bag and use ⅔ of that. Also, to create paper-thin slices of onion that truly melt into almost a jam of sorts, I highly recommend using/purchasing a mandoline. I don’t love single-use tools, but having one of these is worth it, simply due to the time they save you and the precision they allow for when slicing anything and everything.

Note 2: Leftover onion soup concentrate can be stored in the fridge for up to 5 days and in the freezer for up to 3 months.