Preheat the oven to 350°F/180°C. Take your baking dish and grease it with butter.
In a large bowl, whisk together eggs, milk, heavy cream, sugar, cinnamon, and vanilla.
Add bread to the bowl and mix until the bread is completely coated with the liquid.
Cover with plastic wrap and allow the bread to soak in the refrigerator for at least 30 minutes up to 8 hours.
Fold sweet potato into bread mixture.
Pour the bread mixture (including all the liquid) into the greased baking dish.
Bake for 25 to 35 minutes, or until golden brown and set.
Let it cool and serve at room temperature.