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1
Preheat the oven to 425u00b0 F.
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2
In a heavy 10-inch saute pan, melt the butter and olive oil. Place the halved potatoes in the pan cut side-down. Cover and cook over low heat for 10 to 15 minutes, or until the potatoes are tender and lightly browned. Let cool and arrange them, still cut side-down, in a pretty pattern in the pan. Set aside.
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3
In a separate saute pan, prepare the greens for the tart. Warm the olive oil, then saute the diced leek and fennel bulb in it for about 2 minutes.
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4
Add the kale, escarole, salt, black pepper, and red pepper flakes. Add a few tablespoons of water if the greens seem dry. Cover and let them steam for about 8 minutes. Let cool.
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5
To assemble the tart, cover the sauted potatoes with the greens and sprinkle evenly with the Swiss cheese.
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6
Roll out the puff pastry on a floured surface to anywhere between 1/4- to 1/2-inch thick and cut it to fit over the pan, trimming the corners. Tuck any excess pastry into the pan with a knife.
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7
Bake in the oven for 20 to 25 minutes, until golden brown. Let cool for 10 to 15 minutes. Run a knife around the edges to loosen the tart, then invert onto a serving platter. Serve warm or at room temperature.
