In a pot, combine 2 cups of heavy cream and 1 tbsp of vanilla extract (or 1 vanilla pod). If using a vanilla pod, split it open, scrape out the seeds, and add both seeds and pod to the cream.
Warm the cream over low to medium heat for about 15 minutes, stirring occasionally. Avoid boiling.
While the cream warms, whisk 5 egg yolks and 1/3 cup of sugar in a mixing bowl until the mixture is pale, fluffy, and doubled in volume. A hand mixer works great for this—mix for at least 4 minutes.
Once the cream reaches around 176°F (80°C), slowly pour it into the egg mixture while whisking constantly. This gradual process helps temper the eggs and prevents curdling.
Pour the combined mixture back into the pot. Heat it gently over medium heat, stirring continuously with a wooden spoon or spatula, until the custard thickens. Be careful not to let the temperature exceed 180°F (82°C).
Pour the custard into a bowl or individual ramekins. Chill in the refrigerator until set, or enjoy warm for a comforting treat.