Don't be afraid to go 100% whole-grain with desserts; we use all spelt flour here with amazing results. The nutty flour boosts the taste of the butter, spices, and vanilla, unlike all-purpose flour, whose bland nature would dilute those flavors. Be sure to weigh the flour for accuracy; using too much will make the cake dry.
How to Make It
Pour oil into a small skillet or saucepan. Split vanilla pod lengthwise; scrape out seeds. Add seeds and pod to oil. Heat over medium just until pod begins to sizzle, about 3 minutes. Reduce heat to low; cook 5 minutes. Remove from heat. Cool to room temperature. Discard bean pod.
Preheat oven to 350°F. Place softened butter in a large bowl; beat with a mixer on medium speed until light and fluffy, about 2 minutes. With mixer on low speed, add oil mixture. Increase speed to medium, and beat until combined (mixture will not be smooth); scrape down sides of bowl as necessary. Add brown sugar; beat on medium speed until softened and well combined, about 2 minutes. Add eggs; beat until well combined, about 1 minute. Add apples; beat on low speed just until combined.
Whisk together flour, baking powder, cinnamon, nutmeg, cloves, and 1 teaspoon salt. Add flour mixture and evaporated milk alternately to butter mixture, beginning and ending with flour mixture, and beating on low speed after each addition just until combined. Pour batter into a 10-cup Bundt pan coated with baking spray. Bake at 350°F until a wooden pick inserted in center comes out clean, 45 to 50 minutes.
Cool cake in pan on a wire rack 10 minutes. Carefully invert cake onto rack; cool completely.
Stir together powdered sugar, melted butter, and remaining 1/8 teaspoon salt in a medium bowl. Stir in 1 1/2 tablespoons cider until mixture is smooth. If mixture is too thick, stir in 1/2 tablespoon cider. Drizzle over cake.