Makes 6 servings
There is little simpler or more wonderful than this tart, whether you serve it as a starter, for lunch or as part of a pick-what-you-want spread of dishes, indoors or out. While mustard may not be what you think of as a mix-in with tomatoes, it’s what makes this tart remarkable. The crust holds sturdy greens, ripe tomatoes, dabs of sweet ricotta and an egg custard, all compatible together and livelier with the mustard. I like grainy French mustard — sometimes called old-fashioned, or moutarde à l’ancienne — but you can go with smooth Dijon if you prefer (or if that’s what’s in the fridge). What’s really important is its freshness: The mustard should have good color (it shouldn’t have gone brown) and bright flavor. You’re depending on it.
a word on the greens and tomatoes
If you’d like, you can use baby kale or spinach instead of large-leaf greens. And although this tart is best when summer’s tomatoes are ripest, I often turn to the recipe when the season is past. The oven’s heat sweetens the tomatoes and makes them more satisfying than you’d expect.
Working Ahead
You can prebake the crust up to 2 months ahead and keep it, wrapped airtight, in the freezer. You can prep the ricotta and mustard mixtures ahead and refrigerate for up to 6 hours. You can wilt the greens a couple of hours ahead.
Center a rack in the oven and preheat it to 425 degrees F. Place the partially baked tart shell on a baking sheet lined with parchment paper or a silicone baking mat.
Warm the olive oil in a large skillet, preferably nonstick, over medium heat. Toss in the greens, season with salt and pepper and cook, stirring, until they wilt and soften, 1 minute or less. (The wilted greens can be kept at room temperature for up to 2 hours.) Scrape them into the crust, leaving any oil in the skillet.
Remove the little core at the top of each medium tomato and slice the tomatoes. If you’ve got cherry or grape tomatoes, halve them. Lay the tomatoes out on a double layer of paper towels, cover with more paper towels and pat away the excess moisture.
Mix the ricotta with the egg yolk and season with salt and pepper. (The ricotta mixture can be covered and refrigerated for up to 6 hours.)
Whisk together the eggs, cream and mustard; season with salt and pepper. (The mustard mixture can be covered and refrigerated for up to 6 hours.) Pour into the crust. Add the tomatoes, arranging them so that they’re fairly evenly distributed. Finish by spooning dollops of the ricotta mixture over the top.
Bake for about 30 minutes, until the filling is puffed and firm in the center; a skewer inserted into the center should come out clean. Transfer the baking sheet to a rack and let the tart cool for at least 15 minutes before serving, or allow it to come to room temperature — it’s good at any temperature.
Just before serving, if you’d like to give the tart a little shine — the tomatoes look good with a gloss — brush a little olive oil over the surface.
Storing: The tart is best served the day it is made, but if you have leftovers, cover and keep them in the fridge — they’ll make a good snack the next day.