Adapted from Chef Franck
1 sheet Puff Pastry
1 egg yolk
One sheet of puff pastry (you can find puff pastry in the freezer section of the supermarket; there are usually two in a package). Defrost and unfold according to directions on package. You will cut 3 3″ wide strips and 6 1/2″ wide strip from one sheet. If needed you could roll out a little thinner to get the required pieces.
Place thee 3” strips on cookie sheet. I use a half sheet pan and lay them side by side, but you could use something a little smaller.
Beat 1 egg yolk with 1 tbs water to make an egg wash
Brush 1/2 inch on the long sides of the strips with the egg yolk mixture
Place ½ inch strips on the top of the egg wash along the sides of 3” strips You are making an edge along the long sides to hold the filling
Egg wash top and sides
Spread thin layer of Dijon mustard
Place thin layer of Swiss cheese on top of mustard
Slice tomatoes (if large cut in half) and fan onto the length of the pastry, overlapping slices
Drizzle small stream of olive oil topped with salt pepper and thyme
Bake in 375 degree oven for ½ hour