Cook sweet potatoes in large pot of boiling salted water until just tender but still firm, about 15 minutes. Drain and refrigerate until cold, at least 2 hours. (Can be made 1 day ahead. Keep refrigerated.)

Line large baking sheet with parchment paper.

Peel potatoes and coarsely grate into large bowl. Stir in green onions.

Whisk eggs, flour, salt, and pepper in small bowl. Gently mix into potato mixture.

Form mixture into 48 walnut-size balls. Transfer to prepared baking sheet. (Can be made 6 hours ahead. Cover and refrigerate.) 

Heat 3 tablespoons oil in large nonstick skillet over medium-high heat.

Place 8 potato balls in skillet, pressing each gently with spatula to flatten to 1 1/2 inch diameter. Cook until pancakes are rich golden brown, about 2 minutes per side. Transfer to paper towels to drain.

Repeat with remaining potato balls, adding more oil to skillet if necessary. Transfer pancakes to platter.

Top each pancake with 1 teaspoon sour cream and scant 1/4 teaspoon caviar. Garnish with chives.

Serve warm or at room temperature.

You can form the sweet potato pancakes up to six hours ahead, leaving only a quick frying before serving.