These roasted tomato and brie tarts have all the buttery, flaky crunch of croissants, but take a fraction of the effort, thanks to this simple recipe. They get additional richness from crème fraîche in the dough.
Put flour, baking powder, and salt in the bowl of a food processor. Pulse a few times to combine. Add cold butter, and pulse a few more times until it looks like a rustic cornmeal. Add the cold crème fraîche, and pulse a few times until the dough just comes together. Turn the dough out into a mixing bowl. Using your hands, work the dough a little bit more to fully incorporate—it should look "shaggy." Place it on a big sheet of plastic wrap, gather the sides up and press the dough into a ball; flatten slightly and chill in the fridge, at least 1 hour and up to 24. (This is a good time to make the half-dried tomatoes you'll need in Step 4: Halve grape tomatoes, toss with salt, pepper, and olive oil, and bake for 1 hour at 300 degrees F.)
Unwrap the dough and place on a generously floured, clean work surface; flour the dough thoroughly. Whack the dough with a rolling pin a few times to soften it. Starting in the middle, roll dough out to either side to make an even rectangle. Fold the dough in thirds, like a letter. Roll it out again and repeat the folding, add more flour if the dough sticks. This time, rotate the rectangle of dough by 90 degrees before rolling it out and folding again. Roll it out one more time, in the direction of the folds, and fold in thirds. When the laminating is done, roll the dough into a square, starting in the middle of the dough and rolling toward yourself, then away. The square should be roughly 10 inches by 10 inches and ¼-inch thick. Trim the edges of the dough, then cut it into 2½-inch-wide strips. Place the strips on a parchment-lined baking sheet and freeze for 15 minutes, so the dough keeps its shape as it bakes.
Preheat oven to 425 degrees F. Make an egg wash by whisking together the egg yolk and heavy cream. Brush the tarts with the egg wash and parbake, 15–20 minutes. When the tarts are puffy and light brown, remove from the oven and prick all over with a fork; then return to the oven for 10 more minutes.
When the tarts are puffy and golden brown, remove from oven and top with sliced Brie and Half-Dried Tomatoes. Return to the oven and bake until the cheese has just melted, 1–2 minutes. Garnish with thyme and serve family-style.