Mix the oat flour, ground almonds / maize flour, rice flour and baking powder together in a bowl
Put the rest of the ingredients into another bowl and mix until the sugar is well combined. Set aside for 5 minutes so the flax starts to gel
Add the wet to the dry and knead with your hands to form a dough. Add a touch more water if you need to but the dough shouldn't be wet or sticky
Chill it in the fridge while you preheat the oven to gas 4 / 180C / 350°F and line a cookie sheet with parchment paper
Split the dough into 16 balls, place on the cookie sheet and flatten. They won't spread in the oven so flatten to your personal preference. I made mine a bit too thick. Remember you'll be putting 2 together so bitesize is the key word!
Bake until the tops are just set, around 12 minutes
Meanwhile mix the sugar and water in a pan and heat until the sugar dissolves and the mixture turns thick and a nice brown colour, around 5 minutes
Put the rest of the filling ingredients in a bowl and warm slightly in the microwave for a few seconds. Stir to combine
Beat into the caramel mixture in the pan and take off the heat once well incorporated and thickened. Don't let it burn!
Cool the cookies on a wire rack
Let the filling cool until the cookies are cool to the touch then spread it on half of the cookies and sandwich the other half on top
Dust the cookie tops with cocoa powder
Serve immediately. Unfilled you can keep them in a lidded container for up to a week
