In a medium saucepan over medium heat, bring the milk and vanilla beans to a simmer but not a full boil.
In a medium bowl, whisk together the egg yolks, cornstarch, sugar and salt until smooth.
Pour ½ cup of the warm milk into the egg yolk mixture and whisk in until smooth.
Pour the egg mixture through a sieve and into the remaining milk in the saucepan, whisking constantly until combined.
Heat the mixture over medium heat and bring to a slow boil, stirring constantly. Continue whisking, being careful to scrap the bottom and sides of the pan until the mixture becomes thick, about 5-6 minutes in total.
Stir and cook for an additional 30 seconds after it thickens and then remove from the heat.
Stir in the butter until smooth.
Pour the cream into a medium bowl, place plastic wrap directly onto the top of the cream and then refrigerate for a minimum of 2 hours.
Once the pastry cream is chilled, remove from the refrigerator and whisk it to loosen it up. Whip the whipping cream until stiff peaks form. Stir in about ⅓ of the whipped cream into the pastry cream to lighten it up and then carefully fold in the rest of the whipped cream until combined.
Fold in the diced peaches and refrigerate the cream until ready to use.