Beat together the softened butter, vanilla, and sugar until creamy and thick.
Add the flour and use a spatula to form a rough dough.
Grease a 9x9 baking pan with butter and press the dough into the bottom, making it as smooth as possible.
Refrigerate for 15 minutes.
Preheat the oven to 375 degrees F. Put the crust into the oven for 15 minutes or until lightly golden and set.
Make the filling
While the crust is baking, combine the citrus juice and hibiscus and stir. Let steep for 15 minutes or until a the juice is a dark red/pink color.
Beat together the sugar and eggs. Beware you may need more or less sugar depending on the sweetness of the citrus you choose. Oranges will need less sugar than lemons.
Strain the citrus juice into the sugar and egg mixture and discard the hibiscus. Beat together and add the flour and beat until well-combined.
Pour the filling into the baked crust and put back in the oven for 35 minutes or until the filling is set but still a little jiggly. If the top begins to brown too much, place a sheet of foil over the top.
Final Steps
Allow to cool for 20 minutes on the counter and then 1 hour in the fridge at least. Overnight would be best.
Run a knife around the edge of the pan and gently flip the citrus bars out. Top with powdered sugar and enjoy!
