Preheat the oven to 350°F (175°C). Thoroughly grease and flour a 10- or 12-cup Bundt pan, making certain the interior surface is evenly coated to help prevent sticking. Set the pan aside.

Place the yellow cake mix, apple cider, sweetened applesauce, room-temperature eggs, and 2 tablespoons of melted butter in a large mixing bowl. Using a hand mixer on low speed, blend only until the ingredients are incorporated.

Add the packed brown sugar and vanilla extract. Continue mixing just until the batter becomes smooth and evenly combined. Avoid excessive mixing so the finished cake retains a light, tender texture.

Transfer the prepared batter to the greased and floured Bundt pan. If necessary, use a spatula to level the surface.

Bake for 40–50 minutes, checking for doneness around the 45-minute mark. The cake is ready when a toothpick inserted near the center comes out clean.

Remove the baked cake from the oven and place the pan on a wire cooling rack. Allow the cake to rest inside the pan for 15 minutes.

After the initial cooling period, carefully invert the Bundt pan onto a cooling rack or a sheet of parchment paper and release the cake. Let it cool completely before applying the topping.

In a small bowl, thoroughly stir together the granulated sugar and ground cinnamon until the spice is evenly distributed throughout the sugar.

Once the cake has cooled completely, brush the entire exterior with the 1/4 cup of melted butter, covering the top and sides.

Generously distribute the cinnamon-sugar mixture over the buttered surface, making sure the top and sides receive an even coating.