In a medium bowl, mix together all ingredients. Not everyone likes raisins so I either make one batch with and one without, or split the filling after it is mixed and then add raisins in to half.
Place the tart shells on a large rimmed baking sheet. Pour spoonfuls of filling into the tart shells. If you get any on the baking sheet, wipe it up, as it may burn.
Bake at 450°F for 8 minutes, then reduce to 350°F and bake until the pastry is lightly brown, about 5 minutes.
Transfer to a cooling rack and allow to cool completely.
Recipe by Life at Cloverhill at https://lifeatcloverhill.com/2013/04/butter-tarts-recipe.html