Put melted butter (slightly cooled) in a large bowl. Whisk together butter, brown sugar, and granulated sugar until smooth and glossy. Add egg and vanilla. Whisk until combined.
In a smaller bowl, whisk together AP flour, almond flour, salt, and baking powder.
Stir dry ingredients into wet ingredients in three additions until combined. Fold orange zest into the dough.
Chill dough in the fridge for at least 1 hour to firm up the butter. 6-8 hours for deeper flavor.
Once dough is firm, but still soft, scoop out 1 1/2 tablespoon-sized balls of dough and roll them between your hands until smooth. Place on a parchment lined tray and continue until all of the dough has been made into balls.
Transfer tray to the freezer for 30 mins to an hour. (Dough needs to be frozen or very firm)
Once firm, remove the tray and roll each ball in the vanilla sugar before placing on a separate parchment-lined baking sheet. Make sure there's at least 3in of space between cookies. (*If you don't plan to make all the cookies, simply drop the balls in a freezer bag and leave them in the freezer until ready to use.) Bake at 350 for 10-11 mins (depending on your oven) until the edges are golden brown. (Do not overbake! The middles of the cookies will look like they're not quite done. Pull them out anyway. This is how you get those crispy edges and chewy soft centers.)
The cookies will be extremely soft. Leave on the baking tray at room temperature for 5 minutes until the cookies are firm enough to pick up, Move them to a cooling rack to finish cooling. As they sit, they will continue to firm.
These cookies are best the day they're made, but can be stored in an airtight container at room temperature for 3-4 days.