Preheat oven to 375.
Grease a 9-inch springform pan with butter and sprinkle with flour; set aside.
Segment the oranges by cutting off the top stem-end and bottom stem-end of the orange just until the flesh is exposed.
Stand the orange up on one of the flat ends.
Working from top to bottom, cut away the peel and pith by following the curve of the fruit.
Slice out each orange segment by cutting in towards the center of the orange, following the connective membranes. Set aside.
In a medium bowl, whisk together flour, baking soda, baking powder, cinnamon and orange zest. Set aside.
In your mixer's bowl, cream together the butter and sugar; beat until creamy.
Add eggs, one at a time, beating well after each addition.
Beat in sour cream and vanilla and continue to mix until thoroughly combined.
Keeping mixer on low, slowly add flour mixture and continue to mix until well incorporated.
Pour the batter in prepared cake pan and using an offset spatula, spread the batter evenly and smooth it out.
Top with one layer of previously prepared oranges.
Prepare the streusel topping by combining all ingredients in a bowl; stir to combine.
Sprinkle the streusel topping evenly over cake batter and oranges.
Bake for 55 to 65 minutes, or until a toothpick inserted in the center comes out clean.
Cool in pan for 30 minutes and serve.
Cake will last for 3 days, covered, at room temperature.