Whether you're road tripping, picnicking or feeding the soccer team after a game, a crowd-pleasing sandwich is a winning concept. But the bumps along the way are fearsome. We've all had bad sandwiches: The bread is soggy. The fillings and condiments slip and slide. And discrete flavors often become murky and indistinguishable if a sandwich sits around too long.
It doesn't have to be this way. Pan bagnat, literally "bathed bread," is designed for just the kind of sitting around that would ruin a lesser combination. Leave it to the French to fill a loaf of crusty bread with tuna or anchovies, peppers, olives and more, and then bathe the sandwich in vinaigrette and wrap it up, letting its flavors develop over several hours. There is only one way this procedure achieves a glorious, sturdy-not-slimy sandwich: the bread. A baguette with a crackly shell of crust is imperative. Soft bread has no place here.
I began to ponder a variation on the traditional pan bagnat using charcuterie, vegetables and cheese. An antipasti cart spied at a nondescript restaurant in upstate New York sealed the deal. By adding vegetables in the form of eggplant caponata, bookending the meaty filling, I made sure there was no chance of a slippery mess. The sandwich pulled together like the long lost Italian cousin of the original French.
Caponata is more than a sandwich condiment. It's a relish, a side dish, a salad, a carry-me-to-work lunch with a hunk of bread and a wedge of cheese, and a celebration of agrodolce, that delicate balance of sweet and sour. Eggplant caponata recipes vary regionally: Some have nuts, others sport raisins, but I prefer to let the eggplant shine with not much more than tomatoes and a smattering of salty additions.
Buy big, unblemished, taut-skinned purple eggplant, as fresh as possible. Fresher means less potential for bitterness. While the ingredient list may seem long, it's more a pinch of this and a scoop of that, with most of them likely to be lurking in the pantry. Substitute at will: If there are no capers around, add more olives. Change up the vinegar to use that bottle you acquired on vacation. This is a bold condiment party that sings in sweet, salty, acidic tones.
One medium eggplant makes a good helping of caponata, about twice what's needed for the sandwich. Whir half in the blender to make a spreadable condiment. Save the other half in its chunky form. Caponata has a long shelf life, at least a week, and refreshes with a wee drizzle of vinegar and a tiny sprinkling of sugar. It is possible to purchase jarred caponata, but freshly made has a crunch (from celery) unlike any in the jar.
Let's get back to the sandwich. Scoop out and form a trench down the center of each side of the bread, and what goes inside will stay put. Arrange the fillings so the flavors blend yet assert themselves as individuals.
A pan bagnat benefits from a long marination before slicing for serving. Although this sandwich is often pressed, the Italian version is better left to mature without anything to weigh it down. Start the process with a plastic-wrap lined counter, open the bread like a book and set it atop that wrap, fill the trenches, and construct the sandwich. Once done, snugly wrap the baguette with the flavors trapped inside, and refrigerate overnight or carry it away in a picnic basket. By the time you've settled next to a stream and unfurled the blanket, the sandwich will be ready.
I'm partial to slicing the sandwich on the diagonal into two-inch segments using a serrated bread knife. Keep the sandwich wrapped while slicing and then peel away the plastic and tuck the slice inside a picnic-perfect absorbent napkin. Serve with a light, bright red wine, then lie back and stare at the clouds.
• Cathy Barrow is author of "Mrs. Wheelbarrow's Practical Pantry" (W.W. Norton, 2014). She blogs at mrswheelbarrow.com.