In a stand mixer fitted with the paddle attachment, add 1 cup room temperature butter and chopped up 1 1/2 tbsp dried hibiscus. On low speed, beat for a 30 seconds for the hibiscus to infuse into the butter.
Add 3/4 cup powdered sugar, 1 tsp vanilla, and 1/4 tsp salt and beat for a couple of minutes.
Add 2 cups of flour and beat on low speed until it's almost mixed through. Turn off the mixer and scrape down the sides of the dough as needed to completely incorporate all of the flour. Beat until the flour is mixed in.
Form the dough into a ball and wrap it in plastic wrap. Place the dough in the fridge for 30 minutes.
Roll out the dough until it's 1/4" thickness.
Using cookie cutters, cut out shapes of dough and place them on a baking sheet. Form the dough back into a ball and roll out again to make more cookies until the dough is almost gone. (3 times of rolling out the dough is enough) Throw away any excess dough.
Using a fork, gently poke each of the cookies 2 times with a fork in the middle of the cookie. Poking holes in the cookies allows them to evenly bake, and for steam to release from the cookie as it bakes.
Bake cookies for 15-16 minutes at 300 degrees F. Shortbread cookies are a pale color, and the bottom will just barely be turning brown when they are finished cooking. Cool on a cooling rack.