Prep the morels and aromatics. Clean the morels thoroughly, checking inside their honeycomb-like ridges for any grit or bugs (see Note 3). Trim off any tough stems if needed and halve the morels lengthwise. Zest the lemon, mince the shallot, slice the Thai chiles, and thinly slice the shiso.
Cook the morels until deeply browned. Heat a cast-iron skillet over medium-high heat. Add the morels to the dry pan and cook, stirring occasionally, until they release their moisture, the liquid evaporates, and the mushrooms start to brown around the edges, 10 to 15 minutes. They should look darker, slightly crisp in spots, and smell deeply earthy and savory.
Add the aromatics. Add the minced shallot and Thai chiles to the skillet and cook, stirring frequently, until the shallot softens, about 1 minute. Turn down the heat if the shallot browns too quickly.
Make the pan sauce. Reduce the heat to medium-low and pour in the sake, scraping up any browned bits from the bottom of the skillet. Let it bubble for 30 seconds to 1 minute, just long enough to slightly reduce. Add the butter and soy sauce, stirring until the butter melts and the mixture turns glossy and emulsified
Finish the morels. Stir in the lemon juice and minced shiso, then taste before seasoning with salt and pepper. Taste, adding more salt for flavor or more lemon juice for brightness.
Toast the bread. Brush both sides of the bread with olive oil, then toast until golden, crisp at the edges. You can do this in a skillet, toaster oven, or under the broiler, depending on what’s easiest.
Assemble and serve. Spoon the morels and their glossy pan sauce over the toast. Finish with a sprinkle of red pepper flakes, lemon zest, more minced shiso, and a light pinch of fleur de sel.
