1 all-butter puff pastry
2 large heirloom tomatoes (red and yellow)
4 small new potatoes
1 small white onion
1 small red onion
2 garlic cloves
2 slices of prosciutto
3/4 cup mix of Conté and Italian provolone, grated
A handful of fresh thyme and basil
Dijon mustard to taste
1 egg yolk
1. Defrost the puff pastry in the fridge for 2-3 hours.
2. Preheat the oven to 400°F. Boil the potatoes then slice thinly. Thinly slice the tomatoes, sprinkle with salt and allow to drain well. If very juicy, pat them dry with a paper towel before putting them on the tart. Thinly slice the onions into rounds and saute in olive oil and with a pinch of salt until soft and starting to brown. Mince the garlic. Coarsely chop the herbs. Cut the prosciutto into small squares.
3. On a sheet of parchment paper, unfold the puff pastry. Score the edges and prick the inside but not the edges, so that they will puff up. Spread a thin layer of mustard on the tart. Sprinkle with the grated cheese and then the onions. Arrange the tomatoes and potatoes in a decorative pattern and top with the garlic, prosciutto, and herbs herbs. Prepare an egg wash out of the yolk of one egg beaten with 1 teaspoon water. Brush the edges with the egg wash. Cook on a baking sheet in the preheated oven for about 20 minutes, until golden brown. Serve immediately.