1. Heat oven to 350 degrees . Generously coat 1 mini Bundt pan (or 2 pans if you have them) with nonstick cooking spray.
2. Prepare cake mix as per package directions, with butter, eggs, milk and pumpkin pie spice. Spoon batter into Bundt cups, filling each halfway. Bake at 350 degrees for 15 to 18 minutes or until dry to the touch. Cool cakes in pan on a wire rack for 5 minutes, then turn out directly onto rack.
3. Clean pan, coat again with spray and make a second batch of cakes. Let cakes cool completely.Frosting
4. Beat butter in a large bowl until creamy. Gradually add confectioners' sugar and milk. Beat on low speed until good spreading consistency, adding more milk as needed. Beat in vanilla and divide frosting into thirds. Tint varying shades of orange with food coloring.
5. Trim cakes level and sandwich 2 of them with a little frosting. Spread frosting on sandwiched cakes, starting at the bottom and spreading toward top in lines to resemble the ridges on a pumpkin. Place pumpkin in a paper liner. Top with a pretzel piece trimmed to look like a stem. Repeat with all cakes, frosting and pretzels, varying the frosting color for variety.