Step 1Put the cashews in a bowl and cover with water. Cover with plastic wrap and refrigerate to soak overnight.
Step 2Drain the cashews and rinse under cold water. Place the cashews in a high-speed blender (this will need to be done in a couple of batches) and add enough water to cover by an inch. Puree until completely smooth. If needed, pass the cashew puree through a fine strainer to remove any coarse bits; the final "cream" should have the smooth, thick consistency of heavy dairy cream. This makes about 3 cups cream (consistency will depend on the amount of water added while blending, and can vary from just over 2 cups to about 3 1/2 cups; thin as desired).
Step 1Combine the kombu and water in a medium pot and bring to a simmer. Reduce the heat to a gentle simmer and cook 40 minutes. Strain. This makes about 5 cups kombu broth, more than is needed for the remainder of the recipe. The broth will keep, covered and refrigerated, up to 10 days.
Step 1Prepare the stovetop smoker: Spread the chips in the base of the smoker, directly over the burner. Place the drip pan (if using) over the chips, and a rack on top of the drip pan. Place the diced mushrooms on the rack (be sure to use a rack fine enough so the mushrooms don't fall through) indirectly over the chips (do not place the mushrooms directly over the chips, as this can cause them to oversmoke and turn bitter). Cover the smoker with the lid, leaving the smoker open only a couple of inches. (If you do not have a commercial stovetop smoker, you can substitute by using a heavy roasting pan, a cake rack and heavy-duty foil to cover the pan as a lid.)
Step 2Heat the smoker over medium heat just until you see smoke escaping through the opening. Close the smoker entirely and gently smoke just to infuse the mushrooms with smoke flavor, not to cook, 3 to 5 minutes. Be careful not to oversmoke, or the mushrooms will become bitter.
Step 1Heat the oil in a medium-sized soup pot over medium-high heat. Add the onion, celery and potato and sweat, stirring frequently, until softened, 8 to 10 minutes.
Step 2Add the broth, cashew cream and smoked mushrooms. Reduce the heat, and cook over low heat, stirring frequently, for 10 to 15 minutes to develop and marry the flavors. The cashew cream will thicken as it cooks, and you will need to add water from time to time to thin and adjust the consistency. We added about 3 cups water as the soup cooked.
Step 3Season with the lemon juice, Tabasco, salt and pepper. Taste and adjust the seasonings as desired. This makes a generous 2 quarts soup.