In a large bowl, whisk the egg, mayonnaise, dijon, Old Bay together until smooth. Add the crab meat and cracker crumbs. Use your hands, or a spoon if you are squeamish, to evenly distribute all ingredients. The mixture should be able to hold its shape. If it's too dry, add more mayo. If it's too wet, add more Ritz crumbs.
Cover tightly (I like these lids) and refrigerate for at least an hour or up to 24.
Preheat oven to 375. Butter a baking sheet. Use a 1/2 cup measuring cup (rounded if you have it) and portion out the crab cakes on the buttered sheets, about 1-2 inches apart. You should have about 6 crab cakes.
Top each with a sliver of butter.
Bake for 10-15 minutes or until lightly browned and heated all the way through. You can broil them briefly for more color if needed.
Serve immediately or at room temperature.