For the filling: Peel and cut sweet potato into 1/2-inch chunks. Roast in microwave in a covered microwave-safe dish with a few drops of water until fork-tender (8 to 10 minutes).
Combine sweet potato and all filling ingredients in food processor or blender and process until the consistency of creamy peanut butter.
Pecan honey butter: Chop pecans and add to a sauté pan over low heat and toast for a few minutes.
Meanwhile, melt butter over medium heat in a small saucepan. Add honey and pecans. Heat until mixture starts to bubble, stirring periodically, then lower heat and keep warm.
For French toast: Combine egg yolks, sugar, cinnamon, nutmeg, salt and vanilla in a flat-bottom dish. Whisk together until dry ingredients are fully moistened and combined with wet ingredients. Warm milk in microwave until warm (not hot), then add milk and melted butter to egg-yolk mixture. Whisk until combined well.
Spread 1-2 tbsp of the filling between every 2 slices of bread to make sandwiches.
Put 1/2 tablespoon unsalted butter in a large skillet over medium heat. Dip toast sandwiches in custard mixture and soak for 15 to 20 seconds on each side. Cook on griddle or pan for 3 to 4 minutes per side until golden brown. Remove and slice into three slices diagonally; arrange on plates. Top with honey-butter.