In a mixing bowl, combine flour, sugar, melted vegan butter, baking powder, and salt for the cake base. Mix until well combined.
Press the mixture into the bottom of a greased baking pan.
In another bowl, mix together the sugar, melted vegan butter, non-dairy milk, cornstarch, vanilla extract, and salt for the topping. Pour over the cake base.
Bake for 35 minutes or until the top is golden brown and slightly firm.