Off to the side, prepare a large heat proof bowl and a fine mesh strainer. You will use this to strain the cream after cooking it.
In a medium mixing bowl, add the cream, milk, and egg yolks. Whisk until fully combined.
In a medium saucepan, add the sugar, cornstarch, and salt. Whisk until fully combined.
While whisking, slowly add the milk mixture to the saucepan. Whisk until combined and no lumps remain.
Turn the stove to medium heat, and whisk constantly until the cream begins to thicken. You are looking for a pudding-like consistency that coats the back of a spoon. Once the cream has thickened to this consistency, remove from the stove to avoid over-thickening.
Immediately pour the mixture through the fine mesh strainer and into the heat proof bowl. Add the butter and whisk until it is fully incorporated.
Add the vanilla extract, and stir until the mixture is fully combined.
Finally, add the food coloring. Start with one drop of blue and a couple drops of red, then stir fully to see the final color. You are looking to get a bright purple similar to the center of the Strange Bun sprite. I ended up using one drop of blue and about 7 drops of red, however this will vary depending on the pigmentation of the food coloring you are using.
Allow the mixture to cool for 15 minutes, stirring occasionally to prevent a skin from forming. After cooled, press some plastic wrap against the surface of the cream, leaving no air bubbles. Allow the cream to refrigerate for at least 4 hours before using. While the cream is refrigerating, we will work on the puff pastry.