Sweet Potato Tart Tatin

Ingredients

• 1  egg yolk 
• 1 teaspoon thyme leaves fresh
• 1 pinch kosher salt black
• 3 tablespoon real maple syrup 
• 1.5 pound sweet potatoes peeled sliced into 1/8" rounds (try to buy potatoes of relatively even width and few bulges)
• 1 tablespoon butter unsalted thinly sliced
• 1 teaspoon milk whole

Equipment

• frying pan
• baking sheet
• oven
• kitchen towels
• spatula
• oven mitt

Directions

1. Heat the oven to 375 degrees. Line a baking sheet with parchment paper.
2. Place the puff pastry sheet on your work surface and cut out a 10-inch circle. Set the circle onto the prepared baking sheet. Prick the pastry all over with a fork and refrigerate.
3. Pour the maple syrup into a cold 10-inch cast iron skillet. Scatter the butter slices here and there over the maple syrup followed by the thyme leaves.Starting in the center, arrange the thinly sliced sweet potato rounds in a couple layers of overlapping concentric circles right on top of the syrup, butter and thyme. You should get 2 to 3 layers. Season with salt and pepper.Get the cold raw pastry dough from the refrigerator. Carefully lay the dough on top of the sliced sweet potatoes.Tuck the edges in all around the skillet, creating a snug fit.
4. Brush the exposed dough with egg wash.
5. Bake until the edges are deep amber and the pastry is puffed and golden, 40 to 45 minutes.
6. Remove from the oven and cool for 10 minutes.When ready to serve, set a serving plate that’s larger than the skillet upside down on top of the skillet. Using oven mitts or thick kitchen towels in both hands, hold the plate and skillet firmly together in front of you. Quickly invert both the plate and the skillet in one confident motion, letting the tart fall onto the plate. The plate will now be on the bottom and the skillet will be upside down on top. Carefully remove the skillet allowing the tart to settle in one piece onto the serving plate. Be careful as the syrup will be hot. A few potato slices may stick to the bottom; simply remove them with a spatula and replace them on top of the finished tart. The end result will be like a traditional tart with the crust on the bottom and the potatoes on the top. Slice into 8 wedges and serve warm.