1. To make the almond filling, in a medium bowl, or in the bowl of a stand mixer, combine the almond flour, sugar, salt, and orange zest. Mash in the butter until it’s completely incorporated. Stir in the eggs one at a time, along with the rum and almond extract. (The mixture may not look completely smooth, which is normal.) Cover and chill.
2. Line a baking sheet with parchment paper. On lightly floured surface, roll one piece of puff pastry into a circle about 9 1/2-inches (23cm) round. Using a pot lid, plate, or bottom of springform pan as a template, trim the dough into neat circle. Place the dough on the baking sheet.
3. Cover it with a sheet of parchment paper or plastic film, then roll the other piece of dough into a circle, trim it, and lay it on top. Chill the dough for thirty minutes.
4. Remove the dough and almond filling from the refrigerator. Slide the second circle of dough and parchment or plastic from pan so that there is only one circle of dough on the parchment lined baking sheet. Spread the almond filling over the center of the dough, leaving a 1-inch (3cm) exposed border. Place an almond or piece of candied fruit to act as the fève (prize) somewhere in the almond filling, if you wish.
5. Brush water generously around the exposed perimeter of the dough then place the other circle of dough on top of the galette and press down to seal the edges very well. (At this point, you may wish to chill the galette since it’ll be a bit easier to finish and decorate, although it’s not necessary. It can be refrigerated overnight at this point, if you wish.)
6. To bake the galette, preheat the oven to 375ºF (180ºC.) Flute the sides of the dough (as shown in the photo) and use a paring knife to create a design on top. Stir together the egg yolk with the milk and brush it evenly over the top – avoid getting the glaze on the sides, which will inhibit the pastry from rising at the edges. Use a paring knife to poke 5 holes in the top, to allow steam escape while baking.
7. Bake for 30 minutes, or until the galette is browned on top and up the sides. (During baking, if the galette puffs up too dramatically in the oven, you may want to poke it once or twice again with a paring knife to release the steam.) Remove from the oven and slide the galette off the baking sheet and onto a cooling rack. The galette will deflate as it cools, which is normal. Serve warm or at room temperature.