Preheat the oven to 350 F.
In the bowl of a stand mixer use the paddle attachment to beat the butter and sugar together at medium-high speed for 1 minute.
On medium speed, beat in the egg, vanilla, almond extract, baking powder and salt.
Measure the flour correctly (see note) and add to the mixer 1 cup at a time, beating until combined after each addition.
Don't chill the dough! Roll out to exactly 1/4" thick on a clean piece of parchment paper using just enough flour on your rolling pin to prevent sticking. (I suggest a rolling pin with measuring disks.) Aim for a rectangle that is tall and skinny, about 11”x18”.
In a medium bowl use a fork to mix together the butter, brown sugar and cinnamon until combined.
With a frosting spatula spread the filling mixture over the rectangle of cookie dough.
Start at the one of the tall sides of the rectangle and roll the dough tightly into a log. Use a sharp knife to trim each end so it is even. (Eat the trimmings raw or baked!)
Slice the log into 1/4” slices, laying each cookie on parchment lined cookie sheet as you go.
Bake at 350F for 6-7 minutes. The cookies will not be browning at all. They will be dead white but look set.
As each pan of cookies is done I recommend gently lifting the parchment paper holding the cookies out of the pan and setting it on a cooling rack or allowing cookies to cool on baking sheets. Do not disturb the cookies until cool and set.
When cookies are cool whisk together the ingredients for the icing. Drizzle over cookies, allow to set and serve.
Store cookies in an airtight container for up to five days.