Make crêpe batter: Blend all ingredients until smooth. Chill 1 hour.
Cook crêpes: Heat nonstick pan, pour 1/4 cup batter, swirl, cook 1 minute per side. Cool completely.
Prepare pastry cream: Heat milk. Whisk yolks, sugar, cornstarch. Temper, cook until thickened. Stir in butter + vanilla. Chill fully.
Fold in whipped cream to make it silky and light.
Assemble cake: Place crêpe on plate, add 2 tbsp cream, spread, repeat until all layers are stacked.
Chill overnight for perfect texture.
Slice and enjoy the softest, dreamiest vanilla cake ever.