Place 24 RITZ® Crackers in the bottom of a 13x9 inch baking dish, flat side down. Place another 24 RITZ® Crackers in the bottom of another 13x9 inch baking dish. Tear the ham gently with your hands to create tiny strips (they do not need to be perfect) and lay a lightly folded slice on each RITZ® Cracker.
Cut the cheese into 1 inch pieces and place one piece of cheese on top of the ham. Top each mini sandwich with another RITZ® Cracker, rounded side up.
Place the butter in a microwave-safe bowl and microwave until melted, about 45 seconds. Gently whisk in the Dijon mustard, worcestershire sauce, and salt.
Pour the butter mixture evenly over the mini sandwiches, dividing the mixture evenly between the two pans. Sprinkle the poppy seeds and the dried onion flakes evenly over the top.
Bake for 10–12 minutes, or until the cheese is melted and the tops of the Ritz Crackers are lightly golden brown.
Transfer to a serving platter and serve while warm.
Make it ahead: these sandwiches are best served while warm. You can gather/prepare all of the ingredients ahead of time, and then assemble and bake the sandwiches when you're ready to serve them. Change it up: any combination of deli meat and cheese works well here. Roast beef and cheddar, or turkey and colby jack are a few ideas!