Place prepared sweet potatoes in a medium saucepan and cover with water. Add 1/2 teaspoon salt. Bring to a boil, and cook until the potatoes are tender and can be mashed easily with a fork. Drain well and return to the saucepan. Add the honey and 4 tablespoons of the butter and mash until smooth. If possible, puree this mixture in food mill. In a small bowl, combine the milk and eggs and stir in the sweet potato puree. In another bowl, stir together the flour, baking powder, salt and cayenne. Add the dry ingredients to the sweet potatoes and stir until just blended.
Melt the remaining butter and reserve. Heat non-stick skillets over medium-heat and coat with some of melted butter. Drop sweet potato mixture into skillets in 1 1/2-tablespoon amounts. Turn once, cooking until golden and crisp, about 1 minute per side. Transfer to a large baking sheet. Repeat the process with the remaining butter and batter. The pancakes can stand at room temperature for 2 hours. Reheat in a 325 degree F. oven for 5 minutes before serving.
To serve, arrange 3 blinis on a plate and garnish each with a slice of cured salmon, a dollop of creme fraiche and a small spoonful of caviar.