Cut cold butter into small pieces, then use a fork or pastry cutter to cut butter into flour. Stop when you have pea-sized clumps.
Add water one tablespoon at a time, stirring after each addition. Stop when dough clumps together.
Shape dough into a ball with hands, then press into a 1-inch thick circular disk. Wrap with plastic wrap, then chill for at least 1 hour.
After dough has chilled, remove plastic wrap, then lightly sprinkle both sides with flour. Place on lightly floured surface, then roll into a 13-inch circle.
Fold dough in half, then fold in half again. Transfer to tart pan, then unfold and press into pan. Trim off excess with fingers or a knife. Chill for 20 minutes (or freeze for 10 minutes).
Prick chilled dough all over with a fork, then line with parchment paper. Fill pan with pie weights (or rice or dried beans), then bake for 15 minutes or until lightly golden. Remove parchment paper and pie weights, then bake for 5 more minutes.
Prepare Roasted Vegetables:
While tart dough chills, zest lemon, then set zest aside. Cut lemon into 4 quarters.
Combine quartered lemon, butternut squash, mushrooms, and onions on a baking sheet. Drizzle with olive oil, then season with salt and pepper to taste. Mix well. Top with thyme sprigs.
Roast vegetables for 20 minutes, then flip. Continue cooking until veggies are tender and lightly browned, about 15 to 20 minutes more.
Discard thyme sprigs, then taste the veggies and add more salt, if needed. Set aside until crust is ready.
Meanwhile, combine ricotta, egg, garlic, thyme leaves, salt, pepper, and reserved lemon zest in a medium bowl. Squeeze juice from roasted lemon wedges into bowl. Mix well.
Fill and Bake Tart:
Reduce oven heat to 375 degrees.
Spread ricotta mixture in tart shell. Top with roasted vegetables, pressing gently into ricotta.
Bake tart until ricotta is set, about 30 minutes.
Serve tart hot or at room temperature. Enjoy!
There are many steps here, but nothing is difficult to prepare. To keep things moving as smoothly and as quickly as possible, you can work on some of the steps concurrently (like roasting the vegetables while the tart dough chills). Here's a simplified plan to keep in mind:
Prepare the crust, then chill it.
Prep and roast the vegetables while the dough chills.
Roll out the crust and chill it again. Blind bake the crust once the veggies are done roasting.
Make the ricotta filling while the crust cooks.
Fill and bake the tart.
To save more time, you can make the tart dough a couple days ahead of time (or even freeze it up to a month in advance). You could also replace the homemade crust with a premade pie crust.Roast the veggies and blind bake the crust at 425 degrees. Then, make sure to reduce the oven heat to 375 degrees before cooking the tart.This recipe is very flexible and can be made with different vegetables, herbs, etc. Check out the tips before the recipe for lots of ideas.