You can make the creme anglaise and caramel a day ahead of the Bittersweet Chocolate Souffles. Refrigerate the creme anglaise and store the caramel at room temperature in airtight containers.
Prepare an ice-water bath. Whisk together yolks and 1/4 cup sugar in a medium bowl. Bring milk and 1/2 cup cream to a simmer in a medium saucepan. Pour one-third of the hot milk mixture into yolk mixture, whisking until combined.
Pour yolk mixture back into pan. Cook over medium heat, stirring, until mixture coats the back of a spoon, 6 to 7 minutes. Transfer pan to ice-water bath, and let the creme anglaise cool completely.
Put 3/4 cup sugar, 1/4 cup water, and the lemon juice into a medium saucepan over high heat. Bring to a boil, without stirring, and cook until caramel turns dark amber. Remove from heat, and stir in the remaining 1/2 cup cream.
Whisk together creme anglaise and caramel in a medium bowl, and serve.