Heat oven to 170°C (340°F). Grease and flour a 10–12 cup Bundt pan.
Chop oranges, remove stem & seeds. Blend in Solis chopper with oil to a thick smooth paste.
Mix sugar and orange zest; rub between fingers until fragrant. Add butter and whisk until pale & fluffy.
Add eggs one at a time, mixing just to combine.
Fold in orange purée, sour cream, and vanilla.
Add flour, cornstarch, baking powder, baking soda, and salt; fold gently until just combined.
Transfer batter to pan and bake 45–55 min, until a skewer comes out clean.
Boil orange juice, water, and sugar until sugar dissolves; remove from heat.
After 5 min out of oven, poke holes in the warm cake and pour syrup evenly.
After 15 min, release from pan and cool completely.
Whisk glaze ingredients, adding powdered sugar until thick, and spoon over cooled cake.
