Spray a 9x13 with cooking spray. Place the diced honeybuns into the baking dish and set aside.
In a large bowl whisk together the eggs, sugar, butter, cinnamon, and vanilla until combined.
Add the milk and gently whisk it in.
Pour this mixture over the honeybuns and press down with a spoon so the honeybuns are submerged.
Let this sit for 30 minutes to give the honeybuns time to soak up the custard.
Preheat the oven to 350°F.
Bake for 45-50 minutes until the top is browned and puffed.