Peel and shred potatoes, shred (don't peel) zucchini, and dice onions and place in a large bowl. Wring out all the liquid very well, and then dry again with a towel. You want the mixture to be very dry.
Add egg, rice flour and salt and combine.
Heat oil in a large pan over medium-high heat until the oil is hot.
Drop large spoonfuls of the potato-zucchini mixture into the oil in batches, and flatten them down to form ½ inch patties. Brown on one side, about 2 minutes, and then flip and brown the other.
Place on paper towels to absorb any excess oil and sprinkle with more salt.
While the oil is still hot, add capers and fry until crispy. Drain on a paper towel.
To make sour cream, combine sour cream and dill.
Top latkes with dill sour cream and capers!