In a small saucepan, bring 1 cup heavy cream, 1 cup whole milk, and 2 tablespoons Earl Grey tea leaves just to a boil over medium heat. Turn off heat; let steep for at least 30 minutes, but no more than 2 hours.

Once the tea has finished steeping, preheat the oven to 325 (F).

In a medium bowl, whisk together 4 egg yolks, 1/2 cup sugar, 1/2 teaspoon lemon zest, and 1/8 teaspoon salt.

Reheat the infused cream and milk mixture (from the first step), bringing to a gentle boil. Slowly whisk into the yolk mixture, whisking constantly to avoid the yolk from cooking. Strain through a fine sieve into a bowl to extract as much liquid as possible without pressing on tea leaves. Discard the leaves.

Working close to the oven to minimize the risk of spilling water, arrange four 6-ounce jars in a baking pan large enough to hold the cups without touching one another. Pour boiling water into the pan, being careful not to splash any inside the cups, until water comes halfway up the sides ot the cups.

Divide the custard evenly amongst the cups. Cover pan tightly with aluminum foil, poking a few holes to let steam escape. Bake until custards are set but still slightly wobbly in the centers, about 30 minutes.