Begin this recipe 1 day ahead.
Preheat the oven to 125°C.
To make the ice cream, place white chocolate in a baking dish and bake, stirring chocolate around the dish every 15 minutes, for 1 1/2 hours or until golden. Cool slightly, then transfer to an electric mixer with condensed milk and thickened cream. Beat on medium-high speed for 3-4 minutes until soft peaks form. Pour into a 1.5L container and freeze overnight.
The next day, preheat the oven to 180°C and line 2 baking trays with baking paper.
For the cookies, place all ingredients in a bowl and stir until combined. Roll into 12 equal-sized balls, then place, 4cm apart, on trays. Flatten slightly with the back of a spoon. Bake for 12 minutes or until just cooked. Cool slightly on a wire rack (cookies should be eaten warm). Remove ice cream 15 minutes before you serve to thaw slightly.
Sandwich scoops of ice cream between two brownie cookies to serve.