Thaw the frozen puff pastry dough in the refrigerator for about 30 minutes or until pliable and soften the Boursin cheese at room temperature.

Slice the tomatoes into ¼-inch thick pieces, sprinkle with kosher salt, and drain for 20 minutes.

Roll out the puff pastry to ⅛ inch thick and transfer it onto a parchment-lined sheet pan, scoring a ¾-inch border around the edges.

Spread a thin layer of Boursin cheese within the bordered area of the pastry and sprinkle half of the chopped basil.

Layer the drained tomato slices over the cheese, slightly overlapping, and place the sheet pan in the freezer for about 20 minutes.

Drizzle the tomatoes with olive oil and brush the pastry edges with the egg yolk mixture before baking.

Bake in a preheated oven at 400°F for 10 minutes, crumble remaining Boursin over the tomatoes, and bake for an additional 20-25 minutes until golden brown.