Melt 2 tablespoons of butter in the slow cooker with the temperature set on high. Brush the bottom of the cooker with the melted butter.
Place the prepared bread cubes into the cooker.
Whisk together the eggs, buttermilk, milk, Dijon mustard, salt and pepper in a large bowl until completely combined. Pour the milk mixture over the bread in the cooker and stir well to combine.
Add the ham, and the shredded shredded cheese into the cooker and stir (if desired, but not necessary). Top the entire casserole evenly with the cornflake crumbs.
Melt the remaining 1 stick of butter and drizzle it evenly over the contents of the slow cooker. Cover and cook on high for approximately 4 hours, or until the casserole has puffed in volume, turns golden brown, and is completely set in the center when poked with a skewer or knife and it comes out clean.
Uncover and allow the strata to sit for 10 minutes before serving.
If desired, top with chopped scallions and additional shredded cheese (not shown) before serving.
Video
Notes
Store any leftovers in an air tight container for up to 5 days.May be frozen. Store in an airtight freezer bag or container for up to 3 months.Thaw before reheating (uncovered) in a moderate oven or air fryer until hot.