In a blender, blend 4 egg yolks with ¼ cup maple syrup until light and fluffy on medium-high speed. Alternatively, use a hand-held mixer to beat the eggs and syrup until fluffy. Leave this mixture in the blender.
Combine 2 (13.5-ounce) cans full-fat coconut milk, 1 teaspoon grated nutmeg, and ½ teaspoon ground cinnamon in a medium saucepan and heat over medium-high heat until simmering, but not boiling. Be sure to whisk often to prevent the mixture from scalding.
Once you see little bubbles beginning to form on the side of the pan, remove the mixture from the heat. Turn the blender on low and very slowly stream in the hot coconut milk in the hole in the top of the blender (while the blender is running), into the egg mixture. Alternatively, slowly stream in the heated coconut milk while mixing with a hand-held mixer.
Transfer the mixture back to the saucepan over a fine-mesh strainer to catch any lumps that may have potentially formed, and heat, stirring constantly, over medium heat until the mixture coats the back of a wooden spoon and the temperature reaches 160℉.
Once the eggnog has thickened, remove it from the heat. Stir in the 1 teaspoon vanilla extract and optional bourbon if desired.
Allow the eggnog to cool to room temperature, and then refrigerate to chill completely. Once chilled, serve as desired.
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Notes
Sweetener: In place of maple syrup, feel free to use coconut sugar or granulated sugar and increase up to ⅓ cup if you like a really sweet beverage. Storage: Store in the refrigerator for up to 4 days. You may need to blend to incorporate coconut milk solids before serving as coconut milk can solidify quickly in the refrigerator. Coconut Milk: You must use canned coconut milk, and full-fat is best. If you are not dairy-free this recipe works perfectly using whole milk as well.