I had a very similar snack during a visit to Centro Vinoteca in New York City a couple years back. I loved the idea of serving this as an hors d'oeuvres for a dinner party so I started thinking about how I could recreate it at home. I made them for Thanksgiving last year for the first time and they flew off the tray. I've made them a few more times since for various dinner parties and they're always a big hit. The recipe is a bit time consuming, especially roasting the tomatoes, but it's worth the time. —dtorres
Center a rack in the oven and preheat the oven to 250 degrees. Line a baking sheet with foil and pour 2 tablespoons olive oil evenly over the pan. Sprinkle the oil with salt and pepper. Cut each tomato in half ,lengthwise, and remove the seeds. Lay the tomato halves cut side down in the pan. Using a pastry brush, give the tops of the tomatoes a light coat of olive oil. Season the tops of the tomatoes with salt and pepper and a little sugar. Slide the pan into the oven and bake the tomatoes for 2 ½ hours - they should be tender but still able to hold their shape. About half way through the cooking process, carefully turn the tomatoes over. Once the tomatoes are done, pull them out of the oven and allow them to cool to room temperature in the pan. (If you are doing this ahead of time, stack the cooled tomatoes in a jar or other resealable container. Pour whatever oil remains in the pan over the tomatoes and refrigerate until ready.
While the tomatoes are in the oven, prepare the garlic mayonnaise. Combine the mayonnaise, lemon juice, and Dijon mustard in a small bowl. Using a microplane, grate the garlic cloves in the bowl and and mix everything together. Transfer the mixture to a plastic squeeze bottle and refrigerate until ready for use. (Note: This makes more than enough for 40 pieces, but I like to use the extra for sandwiches.)
For the crostini you can either use store-bought or make your own. If you're making your own, slice the baguette at a 45-degree angle into roughly 1/2 inch slices and arrange them on a sheet pan. Brush them lightly with olive oil and bake at 375 degrees for 12-15 minutes.
Bake the pancetta on a cookie sheet in an oven preheated to 450 degrees for about 10-15 minutes. Once the pancetta is crisp, place them on a paper towel or wire rack to cool and drain any excess fat.
To assemble, place a confit tomato on each crostini (cutting them to fit, if necessary). Place a dot of the garlic mayonnaise on each tomato to allow the pancetta to stick. Break off a piece of pancetta and place on each crostini atop the tomato. Squeeze the garlic mayonnaise over the tomato and pancetta and then place a bit of frisee lettuce on top.