To make the whipped mascarpone, add the mascarpone to a bowl and using a whisk or a fork, beat it until soft.
Beat in the honey and 1 1/2 tbsp vanilla until just combined.
Slice the bread in 1 inch slices and smear the mascarpone on, as if making a sandwich. Pinch the edges together so the mixture doesn’t come out while cooking it.
In a shallow, medium size bowl, whisk together the eggs, milk, vanilla, cinnamon, nutmeg, rum (if using) and salt until combined. Dip the stuffed bread into the egg mixture, allowing each side to sit for 1-2 minutes in the egg mixture.
When ready to cook the French toast. Heat a large skillet or griddle over medium heat and coat generously with ghee, butter or coconut oil. When the skillet is hot, cook the French toast in batches (do not overcrowd) until golden and crisp, 3 to 4 minutes per side. Remove and serve immediately.