A "pain surprise" or surprise bread is a festive staple in France, both from professional caterers at office Christmas parties and made at home for pre-dinner nibbles or New Year's Eve party food. It looks very impressive but is actually very simple to make. Either make or buy a loaf of bread (caterers often use round loaves but square ones are easier to make) and carefully cut off a thin slice on both ends. Using a long knife, cut the inside of the loaf out in one piece by going around the contour of the bread just inside the crust, then cut this into thin slices. (You may find it easier to do this after leaving it in the freezer for a while so it doesn't crumble, if your crumb isn't dense enough.)
Alternate layers of different fillings - traditional options include smoked salmon, tuna and mayonnaise, smoked ham, pâté, Boursin, etc... - but I've also seen sweet versions at kids' parties with Nutella, jam, peanut butter, honey, etc. Put the loaf back together with the lid on to keep it all fresh until you're ready to eat it. It's much more impressive than a plate full of sandwiches !
You can even make it in advance and freeze it, then bring it out a few hours before it is needed, to hep reduce stress levels when you have a million other things to be getting on with !
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