Place the flour, sugar and eggs in a bowl and beat with a whisk.
Melt the butter and chocolate in a pan, stir into the mixture along with the liqueur. Transfer the brownie mix to the prepared tin, sprinkle the muesli over the top.
Approx. 10 mins. in the lower half of an oven preheated to 220°C. The brownies should still be a little gooey inside. Remove from the oven, allow to cool a little, remove from the tin, cut into 18 pieces, leave to cool on a cooling rack.