Heat the oven to 325° F.
Spread the pecans on a baking sheet. Bake until richly browned and toasty smelling, about 10 minutes.
Let cool, then scoop into the food processor and coarsely chop by turning the machine on and off.
Remove about 1 1/2 cups of the nuts and put in a large bowl to use in the filling.
Add half of the Mexican chocolate to the nuts in the food processor and pulse the machine to mix them.
Add bread slices; process until everything is fairly fine crumbs.
Add 1/3 cup of the melted butter and 1/4 teaspoon of the salt.
Process just to moisten everything.
Liberally butter a 13 x 9-inch baking pan, then evenly pat in the crumb crust mixture. Refrigerate while you make the filling.
Add the remaining half of the Mexican chocolate, the chopped semisweet chocolate and the flour to the bowl with the reserved pecans.
In the food processor (you Don't even need to clean it), mix the eggs and sugar until well combined.
Add the corn syrup, pulse a couple of times, then add the remaining 2/3 cup of melted butter, the remaining 1/2 teaspoon of salt and all the vanilla. Process to combine thoroughly, then pour over the pecan filling mixture, stir well and scrape everything into your crust-lined pan.
Bake 40 to 50 minutes or until the bars have pulled away slightly from the side of the pan.
Let cool to room temperature before cutting into 2 inch-squares, dusting with powdered sugar and arranging on an attractive serving platter.Makes 24 bars Source: