In a preheated 400F° oven, bake sweet potatoes for 1 hour. Reserve
In a sauté pan over medium high heat, add 2 tablespoons butter and olive oil. When butter is bubbling, add garlic, green onions, mushrooms, bell pepper and thyme. Sauté for 10 minutes, or until mushrooms are well browned.
Add Cognac to pan, let sit for five seconds and then light a match to it. Flame should burn out after approximately 10 seconds. (Note: keep your distance. If you have a gas stove, be aware that spattering particles will likely cause the alcohol to ignite prematurely as soon as it is poured in the pan. And if you have big hair, keep it under wraps! If flame continues to burn, put it out by placing a lid on the pan).
Transfer contents to a bowl and let cool.
Add panko, egg, zest of the lemon, goat cheese and salt and pepper to taste. Mix thoroughly with a fork.
TO FINISH & SERVE
Preheat oven to 400°F.
Line a muffin tin with 4 foil or paper liners. Generously spray interior of liners with spray oil. Spoon mushroom mixture into liners. Gently press mixture down and flatten level with the top of the tin.
Just before putting mushroom cupcakes in the oven, spoon sweet potatoes out of their skin, transfer to a mixing bowl, cover with aluminum foil and place it over a pot of boiling water for 5 - 10 minutes. When potatoes are steaming hot, add 2 tablespoons butter and a pinch of salt. Blend thoroughly with a fork.
Bake cupcakes for 8 minutes, or until cakes are fully set, yet still moist. Remove cakes from tin immediately so that they do not continue to cook.
Use a piping bag with a star tip, or a table knife to ice the cupcakes with the sweet potato icing.