Begin by sifting together your flour, salt, and baking powder in a mixing bowl and set aside.
In a separate mixing bowl add your cold vegan butter and sugar and use a standing/electric mixer to whip until the butter is creamed (about 2-5 minutes). Once creamed, add in your flax egg and vanilla bean paste and mix to combine.
Next, gradually add your sifted dry ingredients to the standing mixer and mix until a thick cookie dough is formed.
Before removing the cookie dough from the mixing bowl to roll out, generously flour your rolling surface and rolling pin so the dough does not stick to the surface. If you don't have a great surface to roll the dough out on, place the dough between two sheets of parchment paper to roll out. Gather the dough into a ball, place it on the floured surface, and roll it into a ½" thick rectangle. Make sure not to roll the dough too thin else it will not hold while you are rolling up the filling.
In a small bowl mix together your brown sugar and cinnamon from the filling ingredients. Take the filling and sprinkle evenly over the dough. Then, roll the dough from the longer end into a long log very slowly, tucking the filling in as you go so that there are no air pockets. You don't want gaps of air between the dough as they will cause your cookies to spread and lose their shape while baking. If the dough cracks at all while you roll it up, lightly press it back together so it holds and continue rolling.
Lay parchment paper on top of a large baking tray and place the rolled up cookie log on top. Place the tray with the log in the freezer for at least 10 minutes to solidify before cutting.
After 10-20 minutes, remove the dough from the freezer and preheat the oven to 350F. Cut the dough into 18 even slices that are about 1 inch wide.
Lay the slices onto the same baking tray covered in parchment paper, making sure to leave space between each cookie. Bake for 12-14 minutes until firm and very lightly browned. Remove from the oven and let cool on the baking sheet about 5 minutes. Then, move to a cooling rack to cool completely before icing.
While the cookies are cooling, make the icing by combining the powdered sugar, vanilla bean paste/extract, and almond milk in a small bowl. Whisk until a smooth, but thick, glaze has formed. Drizzle over the cooled cookies and let sit 20-30 minutes at room temperature to harden the frosting. Enjoy!