Mix the egg yolks with the sugar in a large bowl. When the sugar has completely dissolved, stir in the mascarpone and vin santo.
Beat the egg whites with a pinch of salt until stiff and then carefully fold into the mascarpone-egg mixture.
Place the mascarpone cream in the fridge for 30 minutes.
Pour the espresso into a large plate and dip each speculaas biscuit into the espresso one by one and then place them next to each other in the baking dish.
Cover the speculoos with the mascarpone cream. Repeat the layering process three times.
Crumble three speculoos cookies and decorate the tiramisu with them.
Leave the tiramisu to rest overnight in the fridge.