When my husband and I acquired our farmhouse in Provence in 1984, our visits were generally limited to weekend getaways from Paris. For the train ride back to the city, a snack was essential, and pan bagnat, or “bathed bread,” the Provençal sandwich found at every bakery and market in the region, became our standby.
1 small bulb fennel, cored and thinly sliced crosswise
1 small cucumber, thinly sliced crosswise
2 hard-boiled eggs, thinly sliced crosswise
8 oil-cured anchovies, drained
10 salt-cured black olives, pitted and halved
Freshly ground black pepper, to taste
Sprinkle tomato slices liberally with salt and transfer to a colander; set aside to drain for 30 minutes. In a small bowl, break up tuna with a fork and stir in scallions and bell pepper; set aside. In another small bowl, whisk together oil and mustard; set dressing aside.
Scoop the insides from the bread loaf and discard or reserve for another use. Place tomatoes evenly over bottom of bread and then top with fennel and cucumbers; spread tuna mixture over top, and then top with egg slices, anchovies, and olives. Pour dressing evenly over ingredients, and season with salt and pepper; cover with top of bread, pressing lightly to compact.
Wrap sandwich tightly in plastic wrap and place on a baking sheet; top with another baking sheet and weight with a cast-iron skillet. Refrigerate for at least 4 hours or overnight. Slice into quarters to serve.