Quickly blanch the raw pistachios in boiling water for about 4 minutes, then drain and squeeze off the skins—the smoother the paste, the better the texture. Blend thoroughly with a few tablespoons of the milk until ultra‑smooth.

In a mixing bowl, whisk egg yolks with sugar until pale and creamy. Stir in cornstarch until fully incorporated.

Heat the remaining milk over medium heat until just simmering and sugar dissolves.

Temper the yolk mixture by gradually whisking in a small amount of hot milk, then return the full mixture to the saucepan.

Cook gently, whisking constantly until the custard thickens and coats the back of a spoon. Remove from heat.

Stir in the pistachio paste until fully blended, then whisk in vanilla extract.

Pour into a bowl and press plastic wrap directly on the surface to prevent a skin from forming. Chill until fully cooled.