In a mixing bowl, combine the mascarpone cheese, double cream, Tate & Lyle granulated sugar, and vanilla extract. Beat until well combined and smooth.
In a shallow dish, mix together the cooled coffee and coffee liqueur (if using).
Dip each ladyfinger biscuit into the coffee mixture, ensuring it is soaked but not overly saturated. Arrange the soaked biscuits in a single layer in the bottom of a rectangular dish or individual serving glasses.
Spread half of the mascarpone mixture over the soaked biscuits, creating an even layer.
Repeat the process by dipping another layer of ladyfinger biscuits in the coffee mixture and arranging them on top of the mascarpone layer.
Spread the remaining mascarpone mixture over the second layer of biscuits.
Sift the cocoa powder over the top of the tiramisu, ensuring it is evenly distributed. You can use a fine-mesh sieve or a tea strainer for this.
Cover the dish with cling film and refrigerate for at least 4 hours, or preferably overnight, to allow the flavors to meld together and for the tiramisu to set.
Before serving, dust the top of the tiramisu with Tate & Lyle icing sugar for an extra touch of sweetness.
Slice and serve chilled. Enjoy!
Tiramisu tastes best when it is chilled and allowed to sit for a few hours or overnight, as it allows the flavors to develop and the biscuits to soften.