To prepare the dough, blend all of the ingredients together. Transfer to a work surface and knead for 2-3 minutes until smooth and soft. Set aside to rest for 30 minutes, covered
To prepare the filling, in a large skillet heat the olive oil and butter with the mushrooms, shallots and garlic over medium heat
Sautè for 6-8 minutes
Add in the chopped chard stems and torn leaves
Season with salt and pepper and sautè for a further 6 minutes Remove from heat
Preheat oven to 375F
Roll out the strudel dough to a very thin rectangle
Place ⅓ of the grated cheese on the bottom ⅓ of the dough Place the mushroom/chard filling on top
Add another ⅓ of the cheese on top
Gently roll up the strudel into a long log
Transfer to a parchment lined baking tray
Coil the strudel or leave as a log
Gently perforate the top of the strudel with cut lines
Brush with egg wash and sprinkle with the remaining cheese Bake for 30-35 minutes until golden brown and bubbling out of the perforation lines
Allow to cool for 8-10 minutes before slicing along the cut lines Serve warm