Preheat the oven to 350°F (180° C).Grease and line the base of a 9×3 baking tin.
To make the brownies:
Melt the butter and chocolate over a pan of simmering water. Remove from the heat and cool slightly. Stir in the sugar, salt and vanilla.Add the eggs, one at a time, in a second bowl, stirring well until blended. Add the flour and cocoa and beat for 30 seconds until smooth.
Spoon the mixture into the tin and bake for 35 – 40 minutes. If you insert a skewer, it should come out slightly sticky.
To make the mint cream:
Add the butter, icing sugar and yogurt to a mixing bowl and beat with a mixer until soft and creamy. Add the peppermint essence a bit at a time, tasting as you go. Different brands have different strengths, and you don’t want to overdo the flavor.
Add the food coloring, drop by drop, and mix well until you have a nice, soft green.
To finish:
Once the brownies have cooled down completely, spread the mint layer over the top. I found it easier to leave them in the tin to do this.
Place in the refrigerator to set while you prepare the chocolate layer.
Melt the chocolate and butter in the microwave or in a bowl over a pan of simmering water. Cool slightly and then spread over the mint layer.Leave to cool until the chocolate layer has set.
To cut into slices, it is easier to dip your knife into hot water to prevent the chocolate layer from cracking.