Preheat oven to 180c.
Cream butter and sugar until pale and fluffy.
Beat in vegan eggs gradually, then add vanilla extract.
Sift in flour and baking powder, beat thoroughly.
Add water and beat until smooth. I recommend using an electric handwhisk or standalone mixer. This should take about 5 minutes.
Scrape into tart tin, smooth top and bake for 25-30 mins
Remove from oven.
Turn oven up to 200c