Heat oven to 425 degrees. Coat a small roasting pan with lard or shortening. Combine flour and salt in a medium bowl. Make a well in the center, and add eggs. Transfer to a food processor fitted with a steel blade. Add milk and 3/4 cup water plus 2 tablespoons water; process until well combined. The batter will be fairly thin and pourable.
Arrange the sausages in the prepared pan so that they are not touching one another or the sides of the pan. Bake for 10 minutes. Quickly pour batter over partially cooked sausages, and bake until the batter is thoroughly cooked, puffed, and crispy brown on top, 30 to 35 minutes. Serve immediately with mustard.