To make maple tarts, you’ll need to start with unbaked tart shells. I am quite happy to use frozen unbaked tart shells that I buy in Canadian grocery stores, but if I didn’t have any on hand, I’d simply use a recipe like this one from the Kitchn, and make my own. Tartlet pans are easy enough to find.
Let’s say you are starting with frozen tart shells. Preheat the oven to 450˚F. Set out the tart shells on a sheet pan. If you’re using frozen tart shells, just set them out; there’s no need to thaw them.
In a 4-cup measuring cup, beat the eggs only until the whites and yolks are well blended. Add the brown sugar, salt, and vinegar; mix well. Finally add the melted butter and maple syrup, and stir until combined.
Pour the batter into the tart shells – you should have just enough to fill each one. Bake the tarts for 7 minutes, then reduce the oven temperature to 350˚F and bake 6-7 minutes longer, until the fillings are bubbling.
Cool before eating. Store maple tarts, covered, at room temperature for 2 days, or in the refrigerator for 5. Bring to room temperature before eating.