Preheat the oven to 175 degrees Celsius.
Grease or line a 20*20 cm baking pan.
Combine oat flour, rice flour, potato starch, cacao powder, salt and baking powder in a bowl.
Whisk together egg, egg white, applesauce, sugar and milk in a bowl, just until combined.
Add the dry ingredients little by little whisking just until combined.
Pour the batter into the lined/greased baking pan. Place in the middle of the oven and bake for 16-20 minutes (depending on how fudgy you prefer your brownies).
Meanwhile add granulated sweetener, fiber syrup and one tablespoon of water in a small pot. Let the sugar dissolve and stir everything together. Bring to a boil, cook until the sugar starts to turn golden brown and caramelized (takes 3-4 minutes), do not stir or the sugar might crystalize. Remove from the heat, let it cool slightly for 1-2 minutes, then pour in the cream gently. Stir to combine, until you have a smooth sauce. Place back on the stove and let the caramel sauce simmer on low heat until it has reduced and thickened slightly. Add roughly chopped nuts, oats and sea salt, stir to combine and let it simmer for 2-3 minutes more.
Remove the baking pan from the oven. Increase the temperature to 200 Celsius degrees.
Pour the Tosca mixture over the brownie. Place back to the oven and bake for 6-10 minutes more. Increase the heat to 220 or turn on the broiler for the last 2 minutes if the Tosca hasn't turned golden brown. Keep a close eye on the brownies and Tosca so it doesn't burn.
Remove from the oven and let the brownies cool completely before slicing.