1To make the custard, in a saucepan, stir together the cream, milk, 2 tablespoons of the sugar, and the salt. Warm over medium-low heat until gently simmering, stirring to dissolve the sugar. In a heatproof bowl, whisk together the egg yolks and the remaining tablespoons of sugar. Whisk in the cornstarch mixture. Slowly pour about half of the warm cream mixture into the yolk mixture, whisking constantly. Scrape the yolk mixture into the saucepan. Cook, stirring constantly, until the custard is thickened and glossy, about 3 minutes. Remove from the heat and stir in the vanilla extract and the butter until melted. Pour the custard through a medium-mesh sieve into a bowl, press a piece of plastic wrap directly onto the surface of the custard, and let cool completely. (You can cool the custard down quickly by setting the bowl in a larger bowl filled with ice water.) Refrigerate until chilled before using; the custard can be kept in the refrigerator, covered, for up to 3 days.
2In a bowl, stir together the strawberries, sugar, and orange zest. Set aside for 30 minutes to macerate. (If you like, reserve a few slices of strawberry and 1/2 teaspoon of orange zest to garnish the finished parfaits.)
3To whip the cream: in the bowl of a mixer fitted with the whip attachment, on medium-high speed, beat the cream, sugar, and vanilla to medium-stiff peaks. Do not overbeat.
4To assemble the parfaits, layer the strawberries, custard, and cookies—in that order—in 7- or 8-ounce jars or glasses. Break up the cookies into bite-sized pieces to make them fit in a single layer in the jars. Top with whipped cream, garnish with strawberry slices and orange zest if you like, and serve.