Whisk together the melted butter, brown sugar, vanilla, vinegar, and eggs in a medium bowl.
Place 18 frozen tart shells on a large baking sheet. Drop about 10 raisins into each tart shell and then distribute the filling mixture evenly on top throughout all 18 tart shells.
Bake the butter tarts in the preheated oven for 20-23 minutes or until the edges of the tart shell are golden brown and the filling has puffed up.
Let cool slightly or to room temperature before serving. Enjoy!
Notes
I enjoy the ease of using premade frozen tart shells but you could make homemade tart shells instead. You could also use gluten-free tart shells to make this recipe gluten-free
This recipe calls for raisins but you can omit them completely or use currants or chopped pecans, walnuts, or almonds instead. You could even try chocolate chips!