Puree plums and banana in food processor until liquefied (if you want it thicker, add another half or whole banana). Sprinkle a very light bit of cardamom over the top, then a bit of allspice, then salt, if desired. Pulse briefly to combine. Taste and adjust, if necessary.
Serve like a smoothie, or like a soup, with some chopped almonds stirred in! The almonds complement the plum perfectly.
Oh, I must add: My mom, who is an omnivore and loves sugary-sweet snacks (always says my food is ‘bland’ and ‘nasty’), tried this; she took the bowl from me and ate ALL of it! Thankfully, I’d already had a bowlful this morning! Maybe I’m slowly winning her over – one snack at a time ;-).