On very low heat, melt the white chocolate in a saucepan. As your chocolate starts to melt slightly, add a can of condensed milk along with the spices and vanilla extract if using. Keep stirring regularly so that the chocolate does not burn.
When the chocolate is melted and the spices have incorporated, the colour of the mixture will change. Keep on low heat until the mixture starts to slightly thicken. Remove from heat.
Fold in the sifted caster sugar, and keep stirring using a spoon or a hand blender. Beat until the caster sugar is fully incorporated.
Pour the fudge mixture into a lined mini roasting tin. Add some sprinkles if desired then refrigerate for at least 2 hours before cutting into squares.
Store in an airtight container in the fridge for up to 3 weeks. Or in the freezer for up to 2 months.