In a 6-cup blender, briefly whir eggs. Add sugar, cream, and milk, and blend. Add flour and salt, and blend 5 seconds. The batter will seem loose; don't worry.

Add melted butter and vanilla, and blend, first on low, then going up to medium to avoid spills, until emulsified, about 30 seconds. Let batter rest at least 30 minutes (or up to overnight).

Melt about 1 teaspoon butter in a heavy-bottomed skillet over medium-low heat. Ladle ½ cup batter into the pan and swirl to form a thin circle. Cook until pancake is lightly browned on bottom and cooked through on top, 3 to 5 minutes (no need to flip).

Spoon preserves down the center and roll the sides up and over, like a crepe. Sprinkle with powdered sugar. Repeat with remaining batter.