For the crumb base: Add the cookies and melted butter to a food processor and pulverize. Divide among 6 martini glasses.
For the pudding: Stir together the sugar, cornstarch and salt in a medium saucepan. Add the milk and egg yolks and whisk to combine. Add the thyme and lemon zest and heat over medium heat, stirring, until the mixture barely comes to a boil. Simmer gently until it’s thickened like custard, 6 to 8 minutes. Remove the pan from the heat and stir in the butter. Divide the pudding among the glasses over the base and chill for at least 2 hours.
For serving: Top each pudding with mounds of whipped cream, then add a handful of blueberries and some mint to each one.