Preheat the oven to 350 degrees. Spray a 9 x 13 pan with nonstick spray and set aside.
Cream together the butter, powdered sugar, and white sugar until light and fluffy.
Beat in the vanilla extract.
In a separate bowl, combine the flour (do not pack in the flour when measuring), baking powder, and salt.
Add the dry to the wet ingredients and stir until combined. It's okay if it is a little crumbly.
Press the shortbread mixture into the pan and spread across the pan evenly. You can go up the sides a little bit if desired.
Bake for 21-24 minutes or until cooked through in the center. You don't want it overdone so it will be soft with the ice cream and frosting layer.
Frosting
In a small saucepan over medium-low heat, combine the butter and brown sugar. Stir until the butter is completely melted and the brown sugar is well combined. Stir in the heavy whipping cream and continue to stir until completely combined. Add in the vanilla.
Remove from heat (it will thicken as it cools) and place in a resealable container in the fridge to chill for at least 45 minutes or until completely cooled through.
Meanwhile cream together the butter and powdered sugar until light and fluffy. Pour in the completely cooled caramel sauce and stir until combined. . Add salt to desired taste preference and then place in the fridge to set up for about 15 minutes.
(The frosting won't be a super thick, "typical frosting", but when frozen it works perfectly with this dessert)
Putting it together.
Spread the frosting over the cooked (and completely cooled) shortbread crust. Place in the freezer for about 10 minutes (It doesn't need to be completely frozen). Remove the ice cream to soften a little bit.
Measure out four cups and spread it over the frosting layer. Don't let the ice cream melt too much, or it will become icy once it is re-frozen.
Place in the freezer and allow to freeze overnight or until hardened completely.
Once hardened, remove and let sit for about 5 minutes and then slice into bars.
Drizzle chocolate and caramel sauce over the bars and decorate with a cherry if desired.