Preheat the oven to 425 degrees Fahrenheit.

Melt 1 tablespoon of butter in the top part of a double boiler over medium-high heat on the stovetop.

Add the finely chopped onion.

Cook, stirring, until the onion is wilted and translucent.

Add the long-grain rice and cook, stirring, for about 30 seconds to toast slightly.

Add the chicken broth, currants, lemon peel, bay leaf, saffron threads, and salt to the rice mixture.

Bring the mixture to a boil.

Cover the double boiler and place it in the preheated oven.

Cook in the oven for exactly 20 minutes.

Remove the double boiler from the oven.

Discard the bay leaf.

Fluff the rice gently with a fork.

Stir in the remaining 2 tablespoons of butter.

Cover the pot.

Assemble the double boiler by placing the pot containing the rice over simmering water in the bottom half.

Let the rice stand in the double boiler until ready to serve, ensuring it stays warm and moist.