Make oleo saccharum: Use a vegetable peeler to remove as much of the peel from your limes and lemons, avoiding the white pith below the skin. Combine all citrus peels and the sugar in a medium resealable container, seal tightly, and shake to coat the peels in sugar. Let sit at room temperature for at least 3 hours, and up to 8 hours, shaking the container occasionally.
When ready to prepare drink, open container and add tequila. Reseal and shake vigorously, until most or all of the sugar has dissolved. Strain mixture through a fine mesh strainer into blender, pressing on citrus peels to release oils.
Add cream of coconut, fresh lime juice, and 3 ½ cups ice (in that order) to blender. Blend until smooth. If a thicker consistency is desired, add more ice and blend again until smooth. Divide into glasses, top with nutmeg, and garnish with lime round.
