Crepes - Blend first 4 ingredients and 1 TBSP butter in a blender and let sit for 1/2 hour. Heat skillet to moderately high temperature and pour 1/3 cup of crepe batter into buttered skillet. Swirl to cover, and when lightly brown on bottom, turn over and brown other side. Brush with additional melted butter between crepes. Crepes can be wrapped and refrigerated until ready for use.
Vanilla Pastry Cream - Bring 2 cups of milk to a boil. Remove from heat, add vanilla, and set to the side for 10 minutes. Whisk the egg yolks with sugar and cornstarch. Gradually whisk in the hot milk and place pan over moderate heat, stir continuously until custard thickens and just starts to boil. Remove from bath, let cool slightly and gradually stir in butter. When completely cool, cover and refrigerate.
Pear Souffle - Whisk pear marmalade and elderflower syrup into 1 cup of warmed vanilla pastry cream. Whisk egg whites and sugar over a pan of steaming water until frothy. Transfer to mixer and mix until meringue forms stiff (but not dry) peaks. Whisk 1/3 of meringue into pastry cream, and then using a spatula, gradually fold in the remaining meringue.
St. Germain sauce - whisk remaining 1 cup vanilla pastry cream (warmed) with St. Germain liqueur.
Assembly - Heat oven and 2 baking sheets to 400 degrees. Lay 3-4 crepes on each sheet. Place 1/2 cup souffle in the center of each crepe, and gently fold in half, without pressing. Bake until the souffle has set @ 6-7 minutes. Transfer to warmed plate, and dust with powdered sugar. Serve with St. Germain sauce.