Adjust the rack in your oven so that it is in the bottom third of the oven.
Pre-heat the oven to 450°F.
Use a mixer and mixing bowl to cream the butter and brown sugar together until light and fluffy, about 2 minutes.
Add in the corn syrup, egg, vanilla, vinegar and salt.
Mix until well combined. Set aside.
Line the muffin tins with the tart shells.
(Optional) Place a few raisins, currants, walnuts or pecans at the bottom of each tart shell.
Fill each of the tarts about two-thirds full with the corn syrup mixture.
Bake for 12 minutes. The filling should be bubbly and the crust golden brown.
Let the muffin tin stand for about 1 minute on a wire rack.
Then remove the tarts from the muffin tins to prevent sticking.
Put the individual tarts back on the wire rack and let cool completely.
Notes
If you want to make your own tart shells, use our No Fail Pastry recipe. There is a difference between Canadian and American flour so the measurements to make pastry are different depending on which one you use. Our recipe will help to figure out what you need. You can choose either the "really easy" or the "really good" version of the recipe, but the latter works best with these tarts.
For a twist on the traditional Canadian butter tart recipe, substitute maple syrup for the corn syrup which gives it a slightly different flavor.
For firm butter tarts, use 2 eggs instead of 1, increase the brown sugar to ¾ cup and decrease the corn syrup to ¼ cup.
Store butter tarts in an airtight container in the refrigerator for up to 5 days. Bring to room temperature before serving.