In a small sauce pan over medium-low heat, bring apple cider to a simmer. Simmer until reduced by half, about 20 minutes.
Preheat oven to 350 degrees. Butter or use cooking spray to coat the inside of a bundt pan.
Use mixer with paddle attachment to cream butter, sugar, and brown sugar until lightened and fluffy, about 2 minutes.
Mix in eggs, scraping down sides as needed.
In a small bowl, stir together 1 cup of reduced apple cider(see note below), milk, and grapeseed oil. In another bowl, stir together flour, baking powder, baking soda, cinnamon, nutmeg, all spice, and salt.
Alternate mixing liquid and flour mixture into butter. Do this in about 3 additions, starting and finishing with dry ingredients.
Pour batter into prepared pan. Bake for 45-50 minutes, or until a knife inserted into a center of the ring comes out wiht just a few crumbs. Let cool in pan for 10 minutes before removing. Let cool for at least an additional 15-20 minutes before coating.
When ready to coat cake with topping, melt butter and brush over sides and top of cake. Stir together sugar and cinnamon and evenly sprinkle over buttered cake.