Our spiced butter, called niter kebbeh, at the Ethiopian restaurant I worked at absolutely required four things (other than butter): minced shallots, toasted cardamom, fenugreek and turmeric. Oh, and one other thing — time. Slow cooking is essential to this concoction.
Toast the cardamom, cloves and cinnamon in a dry pan over medium heat until they are aromatic, about a minute.
Cut the butter into cubes.
Toss everything into a heavy pot and turn the heat on low. Let this come to a bare simmer and cook gently for at least 30 minutes. We cooked ours at least an hour. It is vital that the milk solids do not burn. If they do, you have ruined the butter. Watch for browning, and when you see it, turn off the heat.
Strain through cheesecloth and store in a clean glass jar. It’ll last 6 months in the fridge, at least a week on the counter, and forever in the freezer.