Roll the puff pastry into a rectangle about 1/4 inch thick. Slide it onto a baking sheet lined with parchment paper. Trim a 1/4 inch strip off of all the edges. Beat one egg with a few drops of water and brush a light egg wash around the edge of the pastry. Place the strips onto the egg wash, pressing gently to adhere. This makes a thin crust all the way around the galette. Refrigerate while you prepare the remainder of the recipe.
Preheat the oven to 425F. In a small bowl, rub the orange zest into the sugar. Add the softened butter and cream together with a wooden spoon. Crack in the remaining egg and the extract; beat this mixture until light and creamy. Add the almonds, flour and salt. Mix thoroughly.
Remove the pastry from the fridge and spread the frangipane evenly around the bottom. Arrange the rhubarb strips in a row on top, nestling them into the frangipane.
Brush the rhubarb with maple syrup, then place in the middle rack of the oven. bake for approximately 30-45 minutes. I find rhubarb varies with the water content, and ovens always vary. look for the crust to be dark golden and the franginape to take on a little colour.
Remove from oven, cool, and enjoy with sweetened whipped cream or ice cream.
Notes
This galette is on the tart side of things, so I recommend serving it with vanilla ice cream or sweetened whipped cream.