Preheat your oven to 350°F (175°C). Generously grease two 10-cup or 12-cup fluted Bundt pans with butter and dust with cocoa powder, tapping out the excess to prevent a white residue on the finished cake.
In a large bowl, whisk together the all-purpose flour, Dutch-process cocoa powder, baking powder, baking soda, sea salt, and pumpkin pie spice until well combined.
In a separate large bowl or stand mixer, cream 1.5 cups of softened butter and the granulated sugar on medium-high speed for 3 to 5 minutes until light and fluffy.
Add the eggs one at a time, beating well after each addition. Mix in the alcohol-free vanilla extract and the sour cream until smooth.
Reduce the mixer speed to low. Add the dry ingredients in three parts, alternating with the whole milk, beginning and ending with the dry ingredients. Mix just until combined; do not overmix.
Divide the batter evenly between the two prepared Bundt pans. Bake for 45 to 55 minutes, or until a wooden skewer inserted into the center of the cake comes out clean.
Cool the cakes in the pans for 20 minutes before inverting them onto wire racks to cool completely. Once cool, use a large serrated knife to level the flat bottom of each cake so they can be stacked flush.
Prepare the buttercream by beating 2 cups of softened butter with the powdered sugar, heavy cream, and remaining vanilla extract until stiff and smooth. Remove 1 cup of frosting to a small bowl and tint it with black food gel. Tint the remaining frosting with orange food gel.
Place one cake leveled-side up on a cake board. Spread a layer of orange frosting over the top. Place the second cake leveled-side down on top of the first to create a spherical pumpkin shape.
Apply a thin 'crumb coat' of orange frosting over the entire cake and chill in the refrigerator for 30 minutes to set. Apply a final thick layer of orange frosting, using the natural ridges of the Bundt shape to guide your spatula for a pumpkin texture.
Use a small offset spatula to etch a Jack-O'-Lantern face into the frosting. Fill the etched areas with the black-tinted frosting. Place the chocolate-coated ice cream cone upside down in the center hole of the top cake to serve as the stem.