Ever wonder why your at-home grilled cheese sandwich gets crispy, but it never forms the same crunchy crust of a grilled cheese from a diner? With the number of restaurant chefs on TV, in books, online and around the corner, you'd think there'd be no secrets left to tell, but not too many home cooks know that the secret to a crunchy crust is a trick that also adds a layer of flavor to all kinds of diner food. Line cooks the world over keep that secret in squeeze bottles on the shelves above their flat-top grills: some call it "grill grease," but it's also known as "flat-top sauce," "special sauce," or "grill sauce." At its most basic, it's a blend of mayonnaise and club soda, stirred to the consistency of cream, that is squirted onto the grill side of a bun or slice of bread to make patty melts, reubens or grilled cheese. The grill sauce must contain oil or butter (something with a non-stick property) along with some sort of protein, such as eggs, which is why it's often mayonnaise-based. Depending on the application, the grill sauce might be flavored with chili powder, garlic or, as in this case, horseradish. I like to use meat left over from a bone-in baked ham, but deli ham (not processed with honey or brown sugar) works well, too. —betteirene
For the Horseradish Sauce
3/4 cup mayonnaise
1 tablespoon(s) prepared or fresh-grated horseradish
For the Horseradish Sauce: In a medium bowl, stir together mayonnaise, horseradish and sour cream. Add a pinch of salt and taste, adding additional salt if desired. Makes 1 cup. Set aside at room temperature during use, then store leftovers covered in the refrigerator for up to two weeks. The sauce goes well with beef, too.
For the Sandwich: Mix one tablespoon of horseradish sauce with one tablespoon of cream, milk or club soda. Stir until smooth. Spread onto the cut sides of the bun.
Heat a small skillet over medium-high heat. Place bun halves, cut-side down, in skillet and cook until deep golden brown, rotating bun frequently to insure even browning. Remove bun from pan and place, cut-side up, on a serving plate. Place cheese on the bottom of the bun.
Add ham to skillet and heat it through. When hot, place it on top of the cheese. Dollop with the remaining tablespoon of horseradish sauce and the top of the bun; serve immediately.