In a mixing bowl whisk together the flour, cornstarch, salt, garlic powder and cayenne. Stir in the hot sauce and beer or seltzer until a thick but pourable batter forms.
The batter should be thick like pancake batter, but if it appears clumpy or overly thick add more beer, seltzer or water until mixture is thin enough for dipping.
Stir together the panko breadcrumbs and sesame seeds, then pour them onto a plate.
Dip the mushroom slices into the batter, then into the panko sesame mixture to coat.
Heat ½ inch of grapeseed oil in a skillet over medium until hot but not smoking.
Fry the mushroom slices in batches of 4 or 5 pieces for 2-3 minutes on each side until golden brown and crispy.
Drain on paper towels or a wire cooling rack.
Sprinkle with additional salt to taste, if desired. Serve hot.
