Preheat your oven to 375 degrees (if dough is ready to go if not make your dough and when you're ready to roll out, preheat your oven)
Make the dough – In the bowl of your food processor ( you can also use a large bowl and a pastry cutter) add the 2.5 cups of flour, 1 tbsp granulated sugar, 1 tsp salt and pulse to combine. Add 16 ounces of cold cubed butter (2 sticks) and pulse til you get coarse crumbs. Slowly with the motor running stream in approx 1/3 cup ice cold water. (Use just enough til the dough pulls away from the bowl of the processor) Dump the dough onto plastic wrap, form a disc and wrap tightly. Refrigerate 1-2 hours. (Overnight is also great and a time saver if you do it the day before you want to make these)
When you're ready to use the dough take it out off the fridge to soften while you prepare your filling. Melt 4.5 tbsp butter in your microwave in a medium mixing bowl then add 1.5 cups light brown sugar, 2.5 tbsp cinnamon, 1 tsp vanilla extract. Set aside
Cut the dough in half and add powdered sugar to a work surface. Roll the dough into a rectangle shape as evenly as possible (it doesn't need to be perfect as you'll discard the ends anyway)
Spread half the filling along the rolled out pastry dough and roll it up into a log, wrap tightly in plastic wrap and refrigerate at least 3-4 hours. (you could also freeze 1 hour) Repeat this process with the second half of the dough and filling. (You can save the second batch and freeze for another time if you don't need as many cookies)
Remove the chilled dough log, slice and discard the ragged ends and continue slicing into discs 1/3 inch thick. Place 2 inches apart on a cookie sheet and bake 8-10 minutes in your preheated oven. Allow cookies to cool at least 10 mins before frosting.
Brush a thick layer of glaze over top of the cookies and add sprinkles if desired. Allow frosting on cookies to "set" for approx 30 min before trying to stack and pack away. Enjoy!