1. Put the chocolate chopped into irregular pieces together with the butter in a small saucepan and leave it on a very low heat until it has melted, stir it and put it to one side.

2. Place the eggs, sugar, salt and the chocolate oat drink in a large bowl and whisk them all together vigorously. Once it is well-mixed, add the chocolate and butter mixture we have already prepared and mix it all together gently using a spatula.

3. Line a square baking tray with paper and pour the mixture into it. To obtain the marbled effect, mix the marbling ingredients together with a fork and once it is ready, place it on top of the brownie mixture with a spoon, swirling it to create the marbled effect.

4. Once it is ready, place it in a preheated oven at 200º for about 25 minutes. When you take it out of the oven, all that remains is to let it cool, sprinkle a few salt flakes over the top to decorate and enjoy!