Set a mandoline to slice at 1/16”. Slice the beets, zucchini, and sweet potato, using the safety guard. * Require 30 – 36 slices of zucchini & beets, and 45 -54 slices of sweet potato.
Place the sweet potato slices on a microwave safe plate, then microwave on high for 3 minutes. Set aside.
Prepare the crispy sage: Heat olive oil in an 8.5” skillet over medium heat. Add 5-6 sage leaves and cook until crisp, 30 – 60 seconds. Using tongs, remove and place the sage on a paper towel. Sprinkle with salt. Repeat until all the sage is fried. Save the oil for brushing the vegetables.
Preheat the oven to 425°F
Prepare the filling: In a medium bowl, whisk one egg, then stir in the oregano. Add in the cottage cheese and the feta, stir to thoroughly combine. Set aside.
Roll out the puff pastry on a floured surface, to fit a 9" x 12" sheet pan. Line the sheet pan with a piece of parchment paper, then place the pastry on the parchment.
Using a knife, lightly score a line ¾” from the edge of the pastry on each of the four sides. Spoon the cheese mixture evenly on the puff pastry, inside of the scored box.
Layer the zucchini slices into a row down the middle about ⅓ the width of the area covered by the cheese mixture. Over lapping 2 slices wide by 15-18 rows long, should accomplish this. Repeat the process with the beats on one side of the zucchini. Then with the sweet potato slices on the other side. As the sweet potato slices shrink a little when microwaved, I suggest layering them 3 slices wide by 15-18 slices long.
Lightly brush the vegetables with the reserved sage oil.
Brush the border with a beaten egg
Once your tart is assembled, refrigerate it for 15 minutes before baking.
Bake in the preheated oven until vegetables are tender and the crust is golden. 25-30 minutes. Cool on the baking sheet for 5 minutes, then slide the tart, still on the parchment paper, onto a cutting board. Slice into 12 portions.
Garnish with fried sage leaves and a finishing salt.