Add rice, cloves, milk, and whole mace to a small pot and let simmer over the lowest possible heat for about 5 minutes, uncovered. Some of the milk will absorb into the rice. Remove from heat and let sit for 30 minutes. Strain the rice from the milk and toss the rice (or use it to make rice pudding!). Place the milk mixture back into the pot and add spices and sugar, along with a pinch of kosher salt. Stir and heat over medium until the sugar has dissolved. Reduce heat to low and cook uncovered for 5 minutes. Turn off heat and whisk in the powdered gelatin. Let cool to room temperature and pour the mixture into silicone molds that have been placed on a tray or plate to stay level. Loosely cover the molds with a paper towel and refrigerate at least 5 hours, or until fully set (ideally overnight). Carefully remove from molds and enjoy.