Scrub potatoes with vegetable brush under cold running water. Peel potatoes. Grate potatoes with box grater or with food processor. Put grated potatoes in colander and rinse under cold running water for about 1 minute. Drain well, then turn out onto paper towels and pat to dry.
In large mixing bowl, beat egg yolks. Add potatoes, flour and baking powder and mix well. Stir in fennel, shallots, orange zest, thyme, salt and pepper. In large skillet over medium heat, heat oil and butter together.
Working in batches and using a ½ cup measure for each pancake, drop potato mixture into skillet. Flatten slightly with back of spoon and cook until golden brown, about 5 minutes. Turn and brown on second side.
Place cooked cakes on paper towels and keep warm in 250° oven while preparing remaining cakes. Serve warm or cold with smoked salmon, crème fraiche, cream cheese or other favorite topping.
Nutritional Analysis per serving: 439 calories, 5.3 g protein, 34 g carbohydrates, 31 g fat (64% of calories from fat), 197 mg cholesterol, 3 g fiber, 627 mg sodium.