How to Make It
Preheat the oven to 400°. Pierce the sweet potatoes with the tip of a knife and bake for about 40 minutes, or until tender. Turn the oven down to 250°.
Slit the skins and scoop the potatoes into a large bowl. Add the butter and cardamom and beat with an electric mixer at low speed until smooth and fluffy. Season with salt and white pepper. Transfer to a serving dish and keep warm.
In a large deep skillet, heat 1 inch of oil until shimmering. Add half of the shallots and fry over moderate heat, stirring, until crisp, 2 to 3 minutes. Using a slotted spoon, transfer the shallots to paper towels. Sprinkle with salt. Repeat with the remaining shallots. Scatter the shallots over the sweet potatoes and serve.
Make Ahead: The recipe can be prepared 1 day ahead. Store the shallots in an airtight container. Rewarm and rewhip the potatoes; recrisp the shallots in the oven if necessary.