Measure flour, sugar and baking powder into a large bowl. Cut in butter until it forms pea-size balls. Add gently whisked egg yolks and work together with your hands. Form a ball. It will seem crumbly, but it will come together. Cover in plastic wrap and let chill in the refrigerator for 30 minutes.
Cream the butter and sugar together until it is a light yellow. Add the egg, vanilla extract and almond extract and beat until fluffy. Mix the almond flour and all-purpose flour together. Add the flour mixture to the batter. Beat until well combined.
Cut the stalks into 3-inch-long chunks. Cut each chunk into 3 or 4 sticks depending on the thickness of the chunks. In a large bowl, combine rhubarb sticks with orange zest and a mixture of flour, sugar, cinnamon and salt. Make sure the sticks are well-coated.
Preheat oven to 350F.
Roll out dough on a large sheet of parchment to approximately 12-inch in diameter. It will seem crumbly, but keep pushing the crumbly pieces back onto the main dough and continue rolling. It works best to roll the dough between two pieces of wax paper to start.
Spread a layer of almond cream in the centre of the rolled-out pastry in a 9-inch diameter circle the same thickness as the dough, leaving a border of pastry. You will have leftover almond cream. Slide the parchment onto a large flat baking sheet.
Arrange the rhubarb sticks over the almond cream in 3-inch by 3-inch squares. Cut some sticks to completely cover the almond cream circle. Using the parchment paper, roll the bare pastry edge up and over the rhubarb mixture, pleating edges as required, leaving the centre of the pie open.
Brush pastry with beaten egg and sprinkle pastry and rhubarb filling with coarse sugar.
Bake on the lowest shelf of preheated oven for 35 minutes or until pastry is golden brown. You may need to cover the galette with tinfoil to avoid over browning while baking. Allow to stand for 5 to 10 minutes before serving.