Peel and reserve the top section of the butternut squash.
Using a Japanese mandoline, slice butternut squash into half inch rounds.
Reserve rounds and set aside.
Using a medium-sized pot add heavy cream, Chinese five spice, light brown sugar, ground cinnamon, nutmeg and Kosher salt.
Bring to a slow simmer on medium heat, about four minutes.
Immediately add butternut squash rounds and cook until tender, about five minutes. Shut off heat.
Using a muffin tray gently remove rounds using a slotted spoon and fill. Be gentle when filling the pan.
Once muffin pans have been filled with butternut squash rounds cover with aluminum foil add a large heavy bottom skillet or pan on top, press and refrigerate immediately.
Allow to cool for at least two hours.
Once cooled gently remove foil and use a small paring knife to cut around the edges to remove gratin.
Turn pan upside down and allow to come up to room temp. About 20 minutes.
Next, add a spoonful of reserved heavy cream mixture to each gratin.
Using a medium-sized bowl add soft butter, panko, and Gruyere cheese. Mix well and add about one tbs. on top of each serving.
Broil until panko mixture looks golden brown and cheese starts to get melty.
Fry fresh sage leaves for garnish.