In a bowl, combine the flour, sugar and salt. Set aside.
In another bowl, combine the eggs and half of the milk. Add the dry ingredients and whisk until smooth. Whisk in the remaining milk.
In a lightly buttered 8-inch (20 cm) non-stick skillet, cook 8 thin crepes, one at a time, using about ¼ cup (60 ml) of batter for each and browning them on both sides. Set the crepes aside on a plate.
With the rack in the middle position, preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper.
In a skillet over medium heat, soften the onion in the butter. Add the spinach. Continue cooking for about 2 minutes or until the spinach has wilted. Season with salt and pepper. Transfer to a bowl and stir in the cheese and sour cream. Mix thoroughly.
Spread filling on one half of each crepe and fold over twice. Place on the baking sheet. Cook for 8 to 10 minutes or until the cheese has melted.
Serve the warm crepes with the Endive and Apple Salad.