For the custard
In a medium sauce pan, whisk together the sugar, cornstarch, and salt. Slowly whisk in the milk until smooth.
Cook and stir mixture over medium-high heat until thickened and bubbly/frothy. Reduce the heat to medium-low and cook for 2 minutes longer.
Remove the pan from the heat.
Stir in a small amount of the liquid into the egg yolks, whisking to combine.
Then pour the tempered egg yolks into the sauce pan, stirring constantly. Bring this mixture to a boil and cook for 2 minutes longer. Remove the pan from heat.
Gently stir in the vanilla then cool the custard to room temperature without stirring.
Transfer custard to a bowl and gently press plastic wrap onto the surface of the custard. Refrigerate for 1 hour to overnight, preferably.
For the peaches
In a large bowl, toss together the prepared peaches, sugar, ground cardamom, and salt until combined.
Allow mixture to sit at room temperature for 15 minutes before using.
Spoon ¼ cup of peaches into each parfait glass or plastic cup.
Top with 2 tablespoons of custard and 2 tablespoons granola. Repeat layers.