In a large pan, cool onion and celery – stirring often – until vegetables are tender and onion becomes translucent.
Add about ⅔ of the mushrooms, garlic, and chicken broth, bring to a boil. Lower heat to a simmer, cook until mushrooms are very soft – about 10 minutes.
Pour mushroom mixture into a blender or food processor, process til smooth. Set aside.
In the same pan, combine heavy cream with remaining mushrooms and thyme, bring to a boil. Cook for about 5 minutes, or until mushrooms are desired tenderness. Add pureed mushroom mixture, stir until well combined.
Whisk together corn starch and water until smooth. Add corn starch mixture to pan, stirring until very well combined. Turn heat down to low, stirring frequently until sauce thickens.
Once sauce thickens, stir in sliced eggs, season with salt and pepper to taste, remove from heat.
Place one slice of hot toast on a plate, spoon some mushroom soup mixture over it. Top with another slice of toast, and more mushroom soup. Serve immediately.
* If using gluten free bread that is super small (most of them!), you may want to allot 3 slices per serving.