Put tart shells on cookie sheets. Bake at 350 F for 15-20 minutes. Pull out and cool on a rack. Turn off oven, that's all we needed it for.
Boil sweetened condensed milk in a small pot. Mix in Nutella, stir until all melted and blended.
Put a little bit in each tart shell. Chill.
[Dec. 2016. Marina Stern suggested: "Ever made caramel by cooking condensed milk? That, mixed with Nutella, makes an AMAZING filling for the little tart shells. Too sweet for a big pie." So I tried it. Went over well at a Christmas Eve party.]