Trois Fromages L’oignon Doux Tartlettes
⏲ ~46 min total · prep 14 · cook 32 · 4 servings
Snacks⏱ 55 min total🔥 3.3g net carbs⚡ ≈255 kcal/serving~11% of calories from carbs
By the KFI Test Kitchen · Tested & approved by Jason Lieu, KFI recipe editor
Published Sep 15, 2026 · Updated Sep 15, 2026
Ingredients
- 1 1/2 cups fine almond flour
- 5 tbsp butter, divided (3 melted for the crust, 2 for the onions)
- 2 large eggs, divided
- 1/4 tsp kosher salt
- 1 large sweet onion (about 10 oz), such as Vidalia, halved and thinly sliced
- 3 oz cream cheese, softened
- 2/3 cup heavy cream
- 1/2 cup shredded Gruyère
- 2 oz fresh goat cheese, crumbled, divided
- 1 tsp fresh thyme leaves
- 1/4 tsp black pepper
Instructions
- Stir the almond flour, 3 tbsp of the melted butter, one of the eggs, and the salt into a soft dough, then press it thinly across the bottoms and up the sides of 12 cups in a mini tart pan (or a greased muffin tin).
- Bake the empty shells at 350°F for 8 minutes, until they look dry and just set; leave the oven on.
- While the shells bake, melt the remaining 2 tbsp butter in a 10-inch skillet over medium-low and cook the onion 15-18 minutes, stirring every few minutes, until deeply golden, jammy, and reduced by half.
- Beat the cream cheese in a bowl until smooth, then whisk in the second egg, the heavy cream, the pepper, and half the thyme; fold in the Gruyère.
- Divide the caramelized onion among the shells, ladle the custard over each to just below the rim, then dot with the goat cheese and the remaining thyme.
- Bake at 350°F for 14-16 minutes, until the centers puff slightly and hold with a gentle wobble in the very middle.
- Cool 10 minutes in the pan, then twist each tartlet free and serve warm.
Why this recipe works
- Blind-baked shells Eight minutes in the oven dries the almond crust before any filling arrives, so the shells stay crisp under wet custard instead of going soggy.
- Slow onions Fifteen to 18 minutes in butter over medium-low reduces the sweet onion by half and turns it jammy. That long cook is where the tart's depth comes from; no sugar touches the pan.
- The wobble The custard is done when the centers puff and hold with a gentle wobble in the very middle. Pulled there, they finish creamy as they cool in the pan.
Tips for making this recipe well
Press, don't roll
Almond dough presses into the cups more evenly than it rolls. Push it thinly up the sides so each shell holds its shape under the custard.
Keep the onion honest
Stir every few minutes and hold the heat at medium-low. Browned, bitter spots in the onion will read straight through the filling.
Beat the cream cheese alone
Soften the cream cheese and beat it by itself until smooth before anything else goes in. A lump-free base ladles cleanly and stops at a line below each rim without spilling.
Twist them free
After the 10-minute rest, a small twist releases each tartlet whole. Use a thin spatula under any shell that grabbed the pan.
Goat cheese on top
Dot it over the custard instead of folding it in. Baked on top, it stays as distinct pockets of tang against the Gruyère beneath.
Serving suggestions
A Vidalia onion does the heavy lifting here. Slow butter over medium-low for 15 to 18 minutes turns it jammy enough to anchor a three-cheese custard, and each tartlet comes in at 3.3 net carbs. Serve them warm from the pan with the last of the thyme scattered over, beside a glass of dry white wine or a pot of tea. Six make a plate, twelve make a tray, and they travel to a potluck in the pan they baked in.
Storage and meal prep
Cool the tartlets completely, then cover and refrigerate for 3 to 4 days. Warm them in a 350°F oven until the centers heat through; the microwave is faster but softens the crust. The empty shells freeze well for 2 to 3 months before filling, which sets you up for a fast appetizer later. Filled tartlets are best within a day of baking, since the custard softens the crust as it sits.
Variations worth trying
- Leek version Cook sliced leeks in place of the onion, same pan, same slow heat, until soft and golden.
- One shallow tart Press the dough into a single tart pan and blind-bake until dry and set, then fill and bake as one tart.
- Goat cheese forward Divide the full 2 oz of goat cheese across the tops for a tangier finish.
- Herb swap Trade the thyme for finely chopped rosemary in winter or basil in summer.
Frequently asked questions
Can I make the shells ahead?
Yes. Blind-bake them up to 3 to 4 days ahead and keep them covered in the fridge, then re-crisp briefly in the oven before filling.
Why did my custard crack?
It baked past the wobble stage. Pull the pan while the centers still tremble and carryover heat finishes them as they rest.
What if I can't find Vidalia onions?
Any large sweet onion works; the recipe calls for about 10 oz. A yellow onion runs sharper, so give it a few extra minutes in the butter.
How strong is the goat cheese?
It reads as soft tang against the sweet onion and nutty Gruyère. Dotted on top, it stays separate from the custard instead of disappearing.
What's the carb count?
3.3 net carbs per serving as written, with the almond flour crust carrying most of it. The onion and the cheeses add the rest.
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As an Amazon Associate and affiliate partner, Keto Food Ideas earns from qualifying purchases at no additional cost to you. Nutritional values are estimates. Recipes are developed with AI assistance and reviewed by our editors before publishing.
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