Pre-heat oven to 170 degrees celsius (fan-forced). Grease and line a 20cm X 20cm square baking tin with baking paper and set aside.
Place the chocolate and butter into the Thermomix bowl and melt for 3 minutes, 50 degrees, Speed 2. Allow to cool slightly.
Add the eggs and mix on Speed 4, 5 seconds.
Add the sugar, vanilla extract and Baileys and mix on Speed 4, 10 seconds.
Add the plain flour, cocoa powder and bi-carbonate soda and salt and fold mix on Speed 4, 5 seconds. Scrape down the sides of the bowl and mix for a further 5 seconds.
Pour into the prepared tin and bake for 20 minutes or until a toothpick comes out slightly moist. Allow to cool for 20 minutes before frosting.
To make the frosting, melt the butter for 2 minutes, 50 degrees, Speed 2.
Add the vanilla extract, pinch of salt, icing sugar, cocoa powder and Baileys Irish cream and mix for 20 seconds, Speed 4. Scrape down the sides of the bowl and repeat once more (or until smooth and creamy).
Spread the frosting over the brownies, sprinkle over the sea salt flakes and allow to cool completely.
Store in an airtight container at room temperature for up to 5 days.