In the bowl of a stand mixer fitted with the paddle attachment, beat sugars and eggs at medium speed until fluffy and lightened in color, 2 to 3 minutes. Add pumpkin, mascarpone, melted butter, vanilla, and orange zest; beat at medium-low speed until well combined, 1 to 2 minutes, stopping to scrape sides of bowl. (Mixture may look curdled at this point, but batter will come together.)
In a large bowl, whisk together flour, pie spice, baking powder, salt, and baking soda. With mixer on low speed, gradually add flour mixture to sugar mixture, beating just until combined.
Using a small pastry brush, coat inside of a 10-cup Nordic Ware Brilliance Bundt Pan with melted shortening. Spoon batter into prepared pan; forcefully tap pan on counter several times to spread batter into grooves and release as many air bubbles as possible. (The pan will be quite full, but the batter will not overflow.)
Bake until a wooden pick inserted near center comes out clean, 55 to 58 minutes. Let cool in pan for 10 minutes. Using a small offset spatula, gently loosen cake from center of pan. Invert onto a wire rack placed over a parchment-lined baking sheet; let cool completely.
Working quickly, spoon a portion of Mascarpone Glaze over top of cake. Drizzle additional glaze onto and between outer ridges, spreading with the back of a spoon or a small offset spatula to cover completely. (Scoop and reuse excess glaze pooled on parchment paper, if needed.) Garnish with pie spice and pepitas, if desired.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/pumpkin-mascarpone-bundt-cake-mascarpone-glaze/