Put the nutella and eggs into a bowl and beat well. Add the flour and baking powder. Mix well again and spread into the lined tray. Bake for 15 - 20 minutes or till just cooked through. Leave to cool
Make the coffee syrup by putting two heaped tablespoons of instant coffee in a jug. Pour over hot water and stir in the sugar. once dissolved add the 125 ml of liqueur. set aside
Prepare the Tiramisu ( trifle) dish and line the bottom with the sponge fingers. Pour enough coffee syrup over them to soak them. A bit at a time is the best way to go but they do need to be fully soaked.
Chop the hazelnuts ready to add at the end. Also break off a corner of brownie so that you can use that on the top as well.
Beat the yolks with 1 tablespoon of the sugar and the vanilla till light and pale and thickened. Set aside. Then in another bowl beat the cream till soft peak. Put the mascarpone into a bowl and beat just till mixed together then fold through the egg yolks or beat both together gently with a hand mixer till just combined. Then fold through the cream. Now you have a lovely creamy mixture.
Clean the beaters and whisk the egg white and 1 Tablespoon of sugar till stiff and white and fold this gently in two lots through the mascarpone mixture. Now you are ready to assemble.
spread half of the mixture over the sponge fingers. Put chunks of cold brownie on top in a single layer. Splash a little extra coffee onto it. Just a tiny bit (maybe 2-3 Tablespoons)
Cover with the other half of the Mascarpone and smooth over. Sprinkle with the extra piece of crumbled brownie and chopped nuts.
Finally make a Nutella drizzle by putting the nutella in a small bowl and add a couple of teaspoons at a time of coffee syrup. The mix will get claggy and dense before it loosens into a silky smooth drizzle. Remember only a bit of liquid at a time.