Instead of the traditional round loaf, this muffuletta employs an 18- by 13-inch sheet pan of olive oily, salty focaccia. We used Saltie's recipe—but use whichever you like best. You can bake it a day before you build the sandwich; just wrap tightly in plastic or foil.
Make the olive spread. Combine the olives, roasted peppers, celery, capers, parsley, olive oil, vinegar, and oregano in a bowl. Season with salt to taste.
Build the muffaletta. Cut the focaccia in half (so you have two 9 x 13 pieces). Now halve each piece horizontally—a big serrated knife and a slow, sawing motion works best here. Flip the 4 pieces over, so the fluffy interior is facing up. Spread the olive mixture evenly over each. On 1 bottom piece, layer half the meat and cheese in this order: capicola, soppressata, mortadella, provolone. Repeat with the other bottom piece. Cap both with the remaining 2 pieces.
Wrap each sandwich tightly in plastic or foil. Place onto a sheet pan and top with another sheet pan. Load up the top sheet pan with some cans or jars. Weigh down for at least 1 hour (at room temperature) or up to 12 hours (in the fridge).
When ready to serve, cut each half into 8 to 16 pieces (so, 16 to 32 total) and arrange together to reflect the original, slab focaccia shape.
Emma is the food editor at Food52. Before this, she worked a lot of odd jobs, all at the same time. Think: stir-frying noodles "on the fly," baking dozens of pastries at 3 a.m., reviewing restaurants, and writing articles about everything from how to use leftover mashed potatoes to the history of pies in North Carolina. Now she lives in Maplewood, New Jersey with her husband and their cat, Butter. Stay tuned every Tuesday for Emma's cooking column, Big Little Recipes, all about big flavor and little ingredient lists. And see what she's up to on Instagram at @emmalaperruque.