The key to it is ramping up the umami quota. Umami translates roughly as delicious and if you're a savoury food lover then umami could be what you crave. I'm not going to go into too much detail where umami is concerned, mainly because I don't fully understand it myself, the science is far too complicated for me.
Anyway, back to the mushrooms. I slice the shitakes and coat them with a bit of olive oil and salt, then pop them on a baking tray and into the oven at 150C for one hour. You need to give them a bit of a shuffle every now and then. I then leave them to cool as I find the flavour is a lot stronger when they're cold.
Now onto step two. I use two large portobello mushrooms as the body of the beast, removing the stalk so they sit better in the roll. These need to be rubbed with what might be my favourite ingredient; fish sauce. This foul smelling nectar gets added to most of my dishes these days. People look at me funny when I add a good slosh to my ragu or stew, but the only time you notice it is when you don't add it. Food tastes sort of flatter without it ,the dish having less depth.
I allow the sauce with the addition of a bit of salt to soak in for ten minutes or so whilst I turn my attention to the roll.
I use a good crusty roll to provide a bit of resistance and bite and I also butter then grill them. This allows the butter to melt into the bread, and also adds some more crunch.
The portobellos now need to be grilled for 7 or 8 mins till cooked through and then a layer of grated parmesan is added covering the gills of the mushrooms. Pop them back under the grill to melt the cheese and you're set.
As for condiments well that's up to you. I use only english mustard on mine, but tomato sauce is good, as tomatoes are very high in umami. I have tried to make my own tomato sauce using a kilo of cherry tomatoes and although it had a tremendous kick to it, it also tasted like shit so I abandoned it.
So there you go my recipe for the perfect mushroom burger.