We clean the bonito from the north and cut into bite-size pieces, much smaller than when we make marmitako and reserve them. We can ask our fishmonger for this task. Prepare a sauce with the finely chopped onion and when it is well poached, add the homemade tomato sauce.
Lightly sauté the sliced mushrooms and add them to the tomato and onion sauce. We incorporate the beautiful and we turn off the fire so that it cooks in the remaining heat, since afterwards it will be finished in the oven. We also add the béchamel sauce and stir, mixing everything until a homogeneous mixture is obtained.
The color will remain orange like when we make the Aurora sauce, tomato mixture and bechamel sauce. Let it rest while we prepare the puff pastry sheet, bending its ends to make a kind of frame. We cut the folded edge and chop the base with a fork. We bake ten minutes at 180ºC and then we fill the puff pastry sheet with our mixture of bonito, tomato, mushrooms and béchamel, putting it back in the oven.
We leave another five minutes at 180ºC and then we grill at 230ºC for another three or four more minutes. We take the tuna and bechamel cake with puff pastry out of the oven and sprinkle with plenty of fresh parsley very choppy. We serve hot or warm.