In a medium saucepan, combine heavy cream, milk, and sugar. Heat over medium heat, stirring until the sugar dissolves. Do not boil.
In a separate bowl, whisk together the egg yolks, lemon juice, zest, and salt.
Temper the egg yolks: Slowly pour a small amount of the warm cream mixture into the egg yolk mixture, whisking constantly to prevent the eggs from scrambling. Repeat this process until you've added about half of the warm cream.
Pour the tempered egg yolk mixture back into the saucepan with the remaining cream mixture. Cook over low heat, stirring constantly with a wooden spoon, until the custard thickens enough to coat the back of the spoon. This should take about 5-7 minutes. Do not boil.
Remove from heat and strain the custard through a fine-mesh sieve into a clean bowl to remove any lumps.
Pour the custard into individual ramekins or a serving dish. Cover with plastic wrap, pressing the wrap directly onto the surface of the custard to prevent a skin from forming.
Refrigerate for at least 2 hours, or until fully chilled and set.
Serve chilled, garnished with fresh berries or a sprinkle of lemon zest, if desired.
Notes
This recipe can be made ahead of time, making it perfect for entertaining. Enjoy!