Preheat oven to 325 degrees F (170 degrees C).
If using homemade pastry, roll out the pastry nice and thin and cut 8 circles about 5 1/2" diameter, re-rolling the pastry scraps if needed. I had a latte mug that was the perfect size so I used that to cut my pastry. Fit the pastry circles into 8 wells a muffin pan, wobbly edges are totally ok and are authentic for butter tarts.
Add 1 tablespoon of raisins to the bottom of each tart shell.
In a medium bowl, beat together the brown sugar, vegan butter, plant-based milk, cornstarch and vanilla until smooth and creamy. *For a slightly runnier filling use 2 tablespoons of cornstarch and for a thicker filling use 2 1/2 tablespoons of cornstarch. Divide the butter-sugar mixture among each tart shell covering the raisins, about 1 1/2 tablespoons of liquid per tart. The tarts will be about 2/3rd full which is perfect. Optionally, you can top the tarts with pecans or walnuts. I did half with pecans and half without.
Bake for about 23 minutes, the filling will be bubbly and foamy. Remove from oven and let cool completely before serving. You may need to run a knife around the edges of the tarts to help release them from the pan.