In the bowl of your stand mixer, whip the eggs and sugar until the eggs are nearly tripled in volume, very pale, and at ribbon stage.
While that is going, in a small saucepan, melt together your butter and chocolate chips. Stir in vanilla.
Once your eggs are ready, turn the mixer's speed to low, and stream in the butter and chocolate VERY SLOWLY to prevent scrambled eggs. Allow the first couple tablespoons to incorporate completely to temper the eggs a bit.
Turn off the mixer and sift in rye flour, cocoa powder, and salt. Gently fold to combine.
Cover, and chill your dough for 1 hour. Do not chill for longer or it will be too hard to scoop.
Preheat the oven to 350ºF. Line your baking sheet with a silicone mat or parchment paper.
Using a #40 scoop, drop 2-Tablespoon sized balls of dough onto the sheet with 2 inches of space between each one. I was able to fit 9 cookies on a sheet, so I baked in 2 batches.
Bake to 10-12 minutes. Allow the cookies to cool completely on the pan before transferring to a wire rack.
Store in an airtight container for up to 5 days. To prevent the cookies from sticking together, place a bit of parchment paper between each layer.