Pre-heat your oven to 180° Celsius and line two large rectangular 24 x 35cm brownie tins with a long sheet of baking paper each, be sure to leave the ends hanging over the edge to make removal easier.
In a large bowl place the butter and sugar and beat together until pale and fluffy. Add in the eggs, one at a time, beating after each addition to ensure they're well combined. Add in the Vanilla extract and beat again.
Throw the flour in on top, along with the cocoa and stir to combine. Mix thoroughly until you have a soft, fudgey mixture. It's a bizarre thing, it's almost part cookie, part cake, part brownie in texture.
Halve the mixture and tip each into your prepared tins. Take the time now to work it over the base of the tins, attempting to get an even layer. The back of a soup spoon will work fairly well.
Pop straight into your oven for 11 minutes to cook. Keep a close eye on them though. What you're after is a soft to the touch thin cake, that has pulled slightly away from the sides of the tin.
Once cooked leave in the tin for 5 minutes to cool, before lifting out (using those over hanging edges of paper) and leaving on a rack to cool fully.
Pull your ice cream out of the freezer for a few minutes and allow it to soften to a workable condition, don't let it melt too much!
Take a large piece of plastic wrap and lay it across your bench, it needs to be twice the size of one of your cakes. Now carefully place a cake slice into the middle of the plastic wrap, keeping the flattest side underneath.
Start dolling out lumps of ice cream onto this and working quickly, create a fairly even layer across the entire thing. Go ahead and use the entire tub!
Continue to work fast here, as your ice cream may start to melt rather quickly. Take the second piece of cake and invert it on top of the ice cream, push down gently to smoosh together and remove the baking paper.
Wrap tightly in the plastic wrap and place straight into the freezer for a good 3+ hours. The longer they're in the freezer, the yummier they'll be.
When you're ready to serve, remove from the freezer and unwrap. Again, try to work rather quickly here. Using a large serrated knife, like a bread knife, cut your block into sandwich size pieces.
Enjoy immediately! Any leftovers can be re-wrapped individually and stored in the freezer for a month.