Place the softened butter, sugar and vanilla into a large mixing bowl. Mix, using a hand mixer or stand mixer with paddle attachment on medium speed for 1-2 minutes, until butter mixture is light and fluffy. Use a rubber spatula to scrape the sides of the bowl once or twice during the mixing process. Add the egg yolk and continue mixing, scraping the bowl as needed, until well incorporated.
Preheat oven to 350°F / 175°C (Umluft: 155 Grad) and line a large baking sheet with parchment paper.
For a relaxing atmosphere in the kitchen I recommend my personal Elle Republic: Chilled Out Kitchen Tunes or Lounge Kitchen Tunes Playlist on Spotify.