Pour the cold heavy whipping cream into a large bowl and whip with an electric mixer until it begins to thicken.

Add the mascarpone, sweetened condensed milk, and vanilla extract. Continue mixing briefly, just until the mixture becomes smooth, creamy, and thick. Do not overmix.

Combine the hot water and instant coffee and stir until the coffee has completely dissolved. Set aside to cool slightly.

Line a loaf pan with cling film, leaving some overhang around the edges to make it easier to remove the frozen tiramisu later.

Quickly dip each ladyfinger into the coffee and arrange the first layer in the bottom of the pan.

Spread a layer of the cream over the ladyfingers and sprinkle with finely chopped chocolate, if using.

Repeat with another layer of coffee-dipped ladyfingers and cream.

Reserve the remaining cream for the topping.

Cover the pan with the overhanging cling film and place it in the freezer for at least 8 hours, preferably overnight.

Keep the reserved cream covered in the refrigerator.

Once the tiramisu ice cream is completely frozen, remove it from the freezer and carefully peel away the cling film.

Transfer the reserved cream to a piping bag fitted with your preferred nozzle and pipe it over the top.

Dust generously with cocoa powder.

Let the tiramisu ice cream sit at room temperature for approximately 20–30 minutes before serving, depending on the room temperature, so it softens slightly and becomes easier to slice.