Preheat oven to 375 degrees. Bake the sweet potatoes for approximately 1 hour or until tender when squeezed or pierced with a knife. Cool slightly
Meanwhile, in food processor fitted with grating blade, shred apple. Remove and set aside.
Remove skins from potatoes and discard. In food processor fitted with steel blade, process potato pulp, butter, corn syrup, brown sugar, bourbon, cinnamon, nutmeg, and salt. Purée until smooth, scraping down side of bowl as necessary.
Butter a 3-quart flat cssserole or gratin dish. Spread half of the puréed potato mixture in prepared dish. Add shredded apple followed by remaining potato mixture.
Topping and Finish:
Lightly crush raisin bran. Toss with salt. Melt butter, stir and simmer gently until browned. Pour over raisin bran and toss to distribute evenly. Use as topping over casserole.
Bake at 375 until hot....about 30 minutes.
MaryJames dishes it out:
Unlike white potatoes, sweet potatoes should never be baked above 375 degrees. It changes the starch structure
Sweet potatoes can be processed in the food processor, white potatoes cannot.
Brown butter makes everything better.
If mixture is too stiff, add more bourbon!
Can do up to 5 days ahead and refrigerate. Or, do ahead and freeze. Always add the topping when ready to bake.