How to Make It
In a large skillet, toast the cumin and coriander seeds over high heat, shaking the pan, until fragrant and lightly toasted, about 10 seconds. Transfer the seeds to a plate to cool, then grind in a mortar or spice grinder.
Melt the butter in the skillet. Add the onions, garlic, salt and pepper and cook over moderate heat, stirring, until the onions are wilted, about 5 minutes. Reduce the heat to low and cook, stirring occasionally, until the onions are very soft and caramelized, about 15 minutes. Add the toasted spices and cook for 1 minute. Add 1/3 cup of water and simmer until the mixture is thick and jammy, about 5 minutes. Stir in the currant jelly and let cool to room temperature.