Pour the 3 cups of apple cider into a wide saucepan over medium-high heat. Simmer for 20–25 minutes until it reduces to exactly 1/2 cup of concentrated, syrupy liquid. Set aside to cool to room temperature.
Preheat your oven to 325°F (163°C). Generously grease a 12-cup Bundt pan with oil or non-stick spray, ensuring every crevice is coated.
In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, sea salt, 2 teaspoons cinnamon, nutmeg, and allspice until well combined.
In a large mixing bowl, beat the 1 cup of avocado oil, 1 cup granulated sugar, and brown sugar together for about 2 minutes. Add the eggs one at a time, beating well after each addition until the mixture is light and aerated.
Stir the cooled cider reduction, unsweetened applesauce, and alcohol-free vanilla bean paste into the wet ingredients until smooth.
Gradually add the dry flour mixture to the wet ingredients. Mix on low speed or by hand just until no streaks of flour remain; do not overmix, as the batter should be relatively thin.
Pour the batter into the prepared Bundt pan and smooth the top with a spatula.
Bake for 50–55 minutes, or until a toothpick inserted into the thickest part of the cake comes out clean and the top springs back when lightly touched.
Allow the cake to cool in the pan for 10–15 minutes. While cooling, mix the 1/2 cup coating sugar and 1 tablespoon cinnamon in a small bowl.
Invert the cake onto a wire rack. While still warm, brush the entire surface of the cake with the melted butter and immediately toss or sprinkle the cinnamon-sugar mixture over the cake to create a thick, donut-style crust. Let cool completely before slicing.