Shred the zucchini and sweet potato. Press through a fin strainer or cheese cloth to remove excess moisture.
In a mixing bowl, whisk an egg until well beaten, add in the sour cream and mix well. Then fold in the rest of the ingredients except for garnishes and mix well. If it is still to moist, add a little more flour. The mixture should hold together, but not be too runny. At the same time, you don't want it too stiff or it will come out dry on the palate.
Heat oil or butter in a saute pan over medium heat. Scoop the mixture into the oil and press down to flatten. For an appetizer, make them about quarter to half dollar size. If you want to serve as an entree or side dish, make them about 3 to 4 inches. Sear about 1 to 3 minutes per side until they have a golden brown crust and are cooked through. If you make them larger, you may want to brown them in the pan and finish in an oven.
Serve them hot with a dolop of creme fraiche and herb garnish. You can also top with ratatouille, a vegetable or meat stew, or seafood. Experiment and enjoy.