In a small mixing bowl, mix the eggs and the flour, using a fork or whisk to break up any clumps of flower. Whisk in a generous pinch of salt and the milk.
Add 1 tablespoon olive oil to a 9-inch omelet pan over high heat. Heat until the oil is hot, but not smoking. Add 1/4 the egg mixture to the pan and cook the frittata on 1 side until the eggs are cooked and the underside is golden brown. Using a spatula, carefully lift the frittata from the pan and gently lay it on a clean cutting board or work surface, keeping the browned side face down. Let the frittata cool as you work with the fish. Repeat with the rest of the egg mixture, making 4 frittatas.
In a small saute pan, heat the remaining oil until hot but not smoking. Add the garlic, parsley, tuna and anchovies and, using a wooden spoon, stir gently over medium-high heat. The tuna and anchovies will begin to blend into a paste-like mixture. Add the lemon juice and continue mixing until well-combined, about 3 minutes. Remove from the heat.
Gently spread the tuna mixture onto the exposed side of the cooled frittata, leaving a 1-inch border all around. Roll up the frittata, taking care not to crack or open the frittata. Wrap parchment paper around the rolled omelet, and let rest for a few hours in the refrigerator. Slice into bite-sized rounds, keeping the parchment paper intact.
Recipe courtesy of Mario Batali