Preheat oven to 180C.
Grease and line the base of a 36 x 13 centimetre tart tin.
Add plain flour, butter and caster sugar to a food processor and blend. If the mix is too crumbly, add some cold water and mix until you have a dough that is pliable but not too wet.
Turn dough out onto a lightly floured surface and roll out to ½ centimetre thickness. Place dough into the prepared tin, pressing into the base and sides. Trim excess dough and prick the bottom with a fork. Bake for 10-15 minutes or until it is a light golden colour. Set aside to cool in the tin.
Blend the tofu using a stick blender or in a food processor until smooth, then add the other custard ingredients and blend until smooth. Transfer ingredients to a saucepan over medium heat and cook for 10-15 minutes, stirring constantly. The custard is ready when it has a thick, pourable consistency. It will thicken and firm up when it cools. Remove from heat and allow to cool for 10 minutes, stirring occasionally.
Pour custard into tart base and refrigerate until set, approximately 4 hours.
To serve, decorate with raspberries and dust with icing sugar.