Melt 1 tablespoon of butter in a medium saucepan over medium heat. Add the rice and stir constantly for about 2 minutes until the grains turn slightly golden and fragrant.

Pour in the whole milk and heavy cream, stir to combine, and bring the mixture to a gentle simmer over medium-high heat, 3–4 minutes.

Reduce heat to medium-low and cook uncovered for 15–18 minutes, stirring every few minutes, until the rice is tender and has absorbed most of the liquid.

While the rice cooks, whisk together the eggs, sugar, vanilla extract, cinnamon, nutmeg, and salt in a bowl until smooth and slightly pale, about 1 minute.

Temper the eggs: slowly ladle about 1/2 cup of the hot rice mixture into the egg mixture while whisking constantly for 30 seconds.

Pour the tempered egg mixture back into the saucepan, stirring constantly. Cook for 2 minutes over medium-low heat until the pudding thickens and coats the back of the spoon.

Remove from heat and stir in the remaining 1 tablespoon butter and the raisins or currants, if using.

Let the pudding rest for 5 minutes before serving warm, or transfer to a dish, cover with plastic wrap pressed to the surface, and refrigerate for at least 2 hours for a chilled version.