Directions

1. To make the crème fraîche: In a sanitized quart mason jar, combine the cream and buttermilk. Cover the jar tightly with cheesecloth and store it in a cool, dry place for 24 to 30 hours.
2. Remove the cheesecloth and cover tightly with a lid.
3. Store the crème fraîche in the refrigerator for up to 7 days, or until you’re ready to make the tart.
4. To make the crust: Preheat the oven to 375º.
5. In a medium bowl whisk together the honey, water, and egg yolk until combined. Set aside.
6. In the bowl of a food processor, combine the flour, sugar, and salt and pulse to mix.
7. Add the chilled butter and pulse 6 to 7 times just to break up the butter.
8. Add the honey mixture to the dry mixture and pulse until a very loose dough has formed.
9. Turn the dough out onto a lightly floured surface, and gently knead it into a round shape a few inches thick.
10. Wrap the dough in plastic, and chill it in the refrigerator for an hour.
11. To make the tart: In a large bowl, toss all of the filling ingredients together — except the egg and flake salt.
12. On a lightly floured surface, roll out the dough into a 12-inch round, roughly 1⁄4-inch thick.
13. Arrange the rhubarb in one layer on the crust, leaving a 2-inch border around the edge. Note: we arranged ours in a fancy design, but the tart will taste just as delicious if you do something simpler.
14. Fold the edge over the filling, leaving the center open.
15. Brush the crust with the whisked egg, and sprinkle the crust and filling with a little sugar, thyme, and flake salt.
16. Bake for 40 to 45 minutes or until the crust is golden brown. Serve warm or cool with a dollop of crème fraîche.