In a mixing bowl, whisk together one large egg and granulated sugar until pale yellow and frothy, about 3-4 minutes.

Sift in flour and cornstarch into the egg mixture, gently folding until well combined and smooth.

In a medium saucepan, heat 2 cups of whole milk over medium heat until simmering.

Gradually pour the warm milk into the egg mixture, whisking continuously to temper the eggs.

Return the tempered mixture to the saucepan over medium heat, stirring constantly until it thickens, about 3-4 minutes.

Transfer the custard to a bowl, cover with plastic wrap on the surface, and cool to room temperature, about 30 minutes.

Crush 8-10 Oreos into fine crumbs and fold into the cooled custard.

In a separate bowl, whip 1 cup of heavy cream until soft peaks form.

Gently fold the whipped cream into the Oreo-custard mixture until fully incorporated.

Spoon or pipe the mixture into serving cups and refrigerate for at least 2 hours.

Top with pearl sprinkles before serving, if desired.