In a small jug, mix together the coffee, Baileys and boiling water until the coffee has dissolved. Set aside to cool.
For the mascarpone cream: in a stand mixer fitted with the whisk attachment (or a large bowl and electric whisk), whisk together the mascarpone, icing sugar and salt on low speed for about 1 minute - or until just combined. Add the vanilla extract, double cream and the Baileys liqueur and continue to whisk on full speed for about 1-2 minutes or until it has thickened up. You want it to hold its shape but not become over whipped.
Next, using a bread knife, cut the panettone in about 6-8 slices.
Take a large serving dish. Approximately 30x20cm and around 10cm deep.
Cover the bottom of the dish with a layer of panettone slices. Brush generously with the cooled coffee mixture. They should be nicely coated but not to the point of being soggy.
Using a palette knife or the back of a spoon, spread over half of the creamy mixture. Repeat with another layer of panettone slices, coffee soak and the remaining creamy mascarpone.
To decorate: pour the cream into a large mixing bowl and whisk until you have medium peaks and it's holding its shape. Take care not to over whisk. If using an electric whisk, you may like to use a hand whisk towards the end.
Spoon the whipped cream into a piping bag - you can use a piping tip or just leave it plain for little dollops. Pipe dollops over the top of the tiramisu. Cover and chill in the fridge for at least 2 hours, ideally overnight, to firm up.
Just before serving, dust liberally with sieved cocoa powder. Spoon into bowls and enjoy!