This sauce is easily made smooth, with consistent results, when a food processor is used. You may use a blender; however, you will need to do the job in 3 batches.

With the metal blade in place, process the flour and cheeses to a paste consistency. With the machine running, pour the hot liquid through the feed tube. Scrape down the sides of the bowl and then transfer mixture to a saucepan; stir constantly over medium heat for 2 to 3 minutes until smooth and thick.

In a small skillet, sauté the onion in butter until soft and translucent. Add pimiento and stir into the cheese sauce.

Rinse the jalapeños. (The jalapeños may be tempered somewhat by a preliminary 30-minute soaking in cold water. Rinse well before stuffing.) Using scissors, make a small slit halfway down each chile, just long enough to allow the filling to be inserted. Cut away the seeds.

In a small bowl, blend together the filling ingredients.

Stuff all the prepared jalapeños. Then either refrigerate until ready to fry or prepare the batter and fry immediately.

In a small bowl, beat the egg whites until stiff.

In another bowl, using the same beaters, beat the egg yolks, flour, and salt about a minute until pale yellow and thick. Then beat the yolks into the whites.

Dip each prepared chile in the batter. Then, using tongs, deep-fry in oil at 375° until crisp and golden, about 1 minute. Drain on a paper towel while preparing the rest of the chiles.

Serve in a chafing dish over hot water with the sauce available for dipping.