Heat the oven to 375F. Scrub the sweet potatoes, poke each one several times with a fork, and set them directly on the oven rack with a sheet pan on the shelf below to catch drips.

Roast 45 to 60 minutes, until a knife slides through the thickest part with no resistance and dark syrup is bubbling out of the fork holes. Roasting slowly at this temperature converts far more starch to sugar than a fast hot roast, and boiling would leach those sugars into the water.

Cool 15 minutes, then split each sweet potato and scoop the flesh out with a spoon. You need about 1 cup of packed flesh.

Warm the milk to about 150F, hot but not boiling. Warm milk blends smoothly into warm sweet potato, while cold milk causes lumps.

Add 1 cup of the sweet potato flesh to a blender with 1 ½ cups of the warm milk, the sugar and the salt. Blend on medium for 30 to 45 seconds until completely smooth. Do not blend on high for longer, as over blending the starch turns the drink gluey.

Taste and adjust the sweetness, then add the remaining milk a splash at a time until the latte is slightly looser than you want to drink it. It thickens as it cools.

Pour into 2 tall glasses. Dust the surface with ground cinnamon and scatter over the chopped nuts if using.

For the optional cheese foam, whip the cream cheese, heavy cream, milk, sugar and salt together until just thick enough to hold a soft ribbon, then float it on top of each glass.

For an iced latte, blend with cold milk instead of warm and add an extra ¼ cup, then pour over a full glass of ice.