As always, prepare this first. Place a medium or large sieve over a mixing bowl. Set aside the butter in one tablespoon pieces.
Add the soy milk, ¼ cup vanilla yogurt, vanilla extract, and pinch of salt to a small sauce pan. Mix to combine and leave to simmer on medium heat. It will simmer pretty quickly, in only a few minutes.
In a small or medium-sized mixing bowl, combine the sugar, cornstarch, and Just Egg.
Mix with a whisk until evenly combined.
Once the milk mixture has started to simmer, slowly whisk in half of it into the Just Egg mixture.
Next, slowly whisk in all of the mixture from the mixing bowl back into the pot with the remaining milk mixture. Whisk continuously on medium heat to cook and thicken the mixture. It should be thick enough to see the streaks of the whisk in it.
Turn off the heat. Scoop the mixture from the pot into the sieve you prepared earlier. Using a rubber spatula, press it through the sieve to get rid of any lumps in the mix. Don’t forget to scrape the outside bottom of the sieve to get any of the mix that collects there.
Mix in one tablespoon of butter at a time while the mixture is still warm. The butter should melt and incorporate into the pastry cream. Then add in the remaining ¼ cup of yogurt.
Place the pastry cream into a piping bag with a small narrow tip. Allow it to cool in the fridge while you make the eclairs.