1. Preheat oven to 425 degrees F. Spray 1 (24-cup) or 2 (12-cup) mini-muffin tins with vegetable cooking spray.
2. Make tart shells. Mix masa harina and salt in a medium bowl. Add water slowly, stirring mixture with a wooden spoon just until moistened. Add oil and stir until completely combined and mixture holds together, about 1 minute.
3. Shape dough quickly into walnut-size balls. Press flat with heels of hands, then press dough into prepared tin. Press gently with fingers until thin (its OK if sides of tarts are above rim). Trim excess.
4. Bake tart shells at 425 F for 18 minutes, until light brown and crisp. Cool in pan for 5 minutes, then remove from pan and cool on a wire rack for 5 to 10 minutes. Tart shells may be baked a day in advance and stored in an airtight container.
5. Prepare filling. Place refried beans in a medium bowl. Add chili powder, cumin, cayenne, salt, and black pepper. Mix thoroughly.
6. Assemble tarts. Preheat broiler. Arrange cooled tart shells on an ungreased baking sheet. Spoon scant 1 tsp. bean mixture into each shell. Top with a small amount of ground beef, chicken, or chorizo, if using.
7. Prepare topping. Arrange 3 olive slices on each shell and press down gently. Spoon 1/2 tsp. salsa on top of each shell. In a medium bowl, mix together both cheeses. Put a little cheese on top of each tart.
8. Broil tarts 2 to 3 minutes, until cheese is bubbly. Remove tarts from oven onto platter. If desired, top each with a dollop of guacamole, scallions, or roasted red pepper. Serve warm.
Source: Hannaford fresh Magazine, March - April 2009