Grease and line a 9 x 5 inch loaf tin with 3 layers of cling wrap. This will enable you to get the semifreddo out of the tin later.
Using a stand mixer or electric hand mixer, whip the 4 oz mascarpone cheese on medium-high speed until smooth.
Pur in the 1 cup heavy whipping cream and continue whipping until soft peaks form.
Turn down the speed a little and pour the cold 1/2 cup sweetened condensed milk and the diluted 2 tsps instant coffee granules into the whipped cream mix.
Turn up the machine to high speed again and whip until your mixture is thick and makes stiff peaks
Scoop roughly 1/3 or the cream mix into the prepared loaf tin and smooth out to cover the base of the tin.
Pur the 3/4 cup strongly brewed coffee and 1/4 cup brandy into a shallow bowl.
Quickly, dunk the 12 ladyfingers, one at a time, into the coffee and place directly into the loaf tin. Fight the urge to dunk for longer, as they only need seconds in the coffee mix.
Once you have finished a layer of ladyfingers, spoon another 1/3 of the cream mix on top and continue with another layer of ladyfingers.
After 2 layers, add the remaining cream mixture over the top and smooth out. You can bang it on the counter to level it.
Freeze for at least 5 hours or overnight before eating.
To serve, invert on top of your serving platter and dust with cocoa powder. Store the semifreddo in your freezer for up to 6 weeks.