In a 4 quart saucepan, bring cherries and tapioca flour to a boil. Simmer for approximately 5 minutes or until the juice has thickened. Set aside to cool slightly.
Preheat the oven to 350℉
Beat butter for one minute in a stand mixer with the paddle attachment.
Add the sugar and beat again until combined, light, and fluffy.
Beat in the eggs and vanilla.
Add the flour and salt into the mixer. Mix slowly until all of the ingredients are combined.
Grease a 15x11 sheet pan.
Spread 3/4 of the batter evenly onto the sheet pan using a slightly damp spatula.
Bake for 35 minutes.
Remove the sheet pan from the oven and allow to cool for 20 minutes before icing.
In a small mixing bowl, combine the powdered sugar, vanilla, and heavy cream.
Drizzle the icing over the entire cherry bars.
Cut into 28 squares. Can be served warm or room temperature.