Combine milk, flour, cornstarch, sugar, eggs, and melted butter in a blender or food processor and blend until smooth.
Pour the mixture through a fine-meshed sieve into a large bowl. Let sit for 15 minutes.
Heat a little vegetable oil or a small amount of butter in a medium nonstick skillet over medium or medium-low heat. Wipe any excess oil with a paper towel.
Pour 1/4 cup of batter, swirling the crepe batter to coat the bottom of the pan.
Heat gently until the surface becomes matte and small air bubbles appear, roughly 1-2 minutes. Flip with a spatula and cook 30 more seconds until golden brown.
Repeat with remaining batter.
Allow all crepes to come to room temperature before proceeding.
You can prepare the crepes a day ahead. Layer with parchment paper and wrap tightly in plastic wrap. Store in refrigerator.