Place potatoes on a foil lined baking sheet. Bake until tender and starting to ooze sugary syrup, about 1 hour and 15 minutes, depending on their size. Remove from the oven and let sit until cool enough to handle. Cut a slit down each potato and scoop the flesh into a large bowl. Discard the skins.
Add the cream, bourbon, brown sugar, molasses, and salt; beat on high speed with an electric mixer until smooth. Cover to keep warm, or gently reheat before serving.
Melt the butter in a large skillet over medium-high heat. Add the onions, reduce the heat to medium-low, and cook slowly, stirring occasionally, until golden brown and caramelized, 45 minutes to 1 hour. Remove from heat and serve hot.