Heat an air fryer to 350ºF, or arrange a rack in the middle of the oven and heat the oven to 350ºF. Meanwhile, assemble the toast.
Melt 3 tablespoons of the unsalted butter in a small microwave-safe bowl in the microwave. Alternatively, melt the butter in a small saucepan over medium-low heat.
Place the remaining 1 tablespoon unsalted butter, 2 tablespoons of the honey, 1/4 teaspoon kosher salt, and 1/8 teaspoon ground cinnamon in a second small microwave-safe bowl. Microwave until the butter is melted, about 30 seconds. Stir to combine. Alternatively, melt together in a small saucepan over medium-low heat.
Evenly spread 1 tablespoon of the melted butter on 1 slice of the milk bread. Top with 1/3 of the honey butter (about 1 tablespoon) and spread into an even layer. Repeat layering bread, melted butter, and honey butter two more times.
Using a serrated knife and keeping the bread slices stacked, cut the top two bread slices into 9 even pieces; do not cut through the bottom slice of bread.
Air fry or bake (transfer onto a baking sheet first if baking) until the honey butter mixture is ever so slightly bubbling, 8 to 10 minutes.
Serve topped with whipped cream or vanilla ice cream, drizzled with the remaining 1 tablespoon honey.