For the pastry: Combine the flour and salt in a large bowl; then, with a pastry blender, cut in the lard until the texture of fine meal.
Forking briskly, drizzle just enough ice water over the mixture to make it hold together.
Shape into a ball, wrap in wax paper, and refrigerate several hours.
Meanwhile, prepare the filling: In a food processor fitted with the metal chopping blade (or in a blender or electric mixer set at highest speed), buzz the mozzarella, butter, sugar, and cinnamon about 60 seconds non-stop until smooth and creamy; scrape down the work bowl sides with a rubber spatula and beat 60 seconds longer. Note: It will take longer for the electric mixer to reduce the mixture to creaminess - perhaps 3 to 4 minutes of steady beating.
Add the egg yolks, one at a time, beating well after each addition; add the flour and snap the motor on once or twice to blend inches Transfer the mixture to a small bowl, cover and chill several hours.
When ready to bake the queijadas, preheat the oven to 400 degrees.
Divide the pastry in half and roll, first one half, then the other, as thin as paper on a lightly floured pastry cloth with a lightly floured, stockinette-covered rolling pin.
Cut into rounds with a 3 1/2 -inch cutter. Also re-roll and cut the scraps. Fit the pastry into plain or fluted tart tins measuring 2 1/2 inches across the top. Set the tins on baking sheets, then half-fill each tart shell with the cheese mixture.
Bake uncovered for 18 to 20 minutes, just until the filling is puffy and a rich amber-brown. Remove the tarts from the oven, cool until easy to handle; then using a small pointed knife, gently pry the tarts from the tins. Serve at room temperature.