I'd go for "healthy" additions which pack a healthy dose of sugar: carrots, beets, applesauce (as you mentioned), pumpkin, squash, etc. Even Tomato Soup! Yeah, you heard me: http://www.recipegoldmine.com/cookdropR/tomato-soup-cookies.html (ok, it still has a healthy amount of sugar, but come on, the yield is 10 dozen-keep that in mind!)

I love carrots so think these recipes are swell: http://www.tasteofhome.com/Recipes/Carrot-Cake-Cookies and http://www.marthastewart.com/recipe/carrot-cake-sandwich-cookies

Be sure to add extra frosting to make up for all of that virtuous fruit/veggie bounty, though.

I know that a lot of people can get really scared of pie and tart dough, but really, you needn't be.

If you want to buy some mini shells, you can probably find them in most nicer grocery stores--graham and cookie crusts in the baking aisle, frozen shells in the freezer aisle (near where they have the Sara Lee cakes and stuff).

This is a recipe I came across a while back that is French but really surprisingly unfussy and easy: http://www.davidlebovitz.com/2009/05/french-tart-dough-a-la-francaise/ -- and a bit more forgiving than a typical pie dough recipe where you have to be more careful about the temperature of your ingredients and have to let the crust rest for periods before using it.

As for materials: when I make mini tarts, I like to use those little foil shells that they sell at QFC or sometimes I will even use silicone muffin/cupcake cups.