• Preheat oven to 325F degrees and adjust oven rack to middle position. Butter and flour a 10-cup bundt pan. Be sure to get all the nooks and crannies of the pan so the cake doesn't stick.
• In a medium mixing bowl, whisk together the flour, baking powder, baking soda, and salt.
  2 ½ cups all-purpose flour, 2 teaspoons baking powder, ¼ teaspoon baking soda, ¼ teaspoon salt
• In a food processor fitted with the blade attachment (a smoothie blender will also work), pulse the prepared chunks of oranges until only small flecks of the rind remain - the mixture should be smooth but not fully pureed.  
  2 large navel oranges
• In the mixing bowl of a stand mixer fitted with the paddle attachment, (or large mixing bowl for hand-held mixer), cream the butter and sugar on medium speed until light and fluffy - about 3 to 5 minutes.  Add in one egg at a time and beat until incorporated after each.   Add the vanilla extract with the last egg.
  12 tablespoons unsalted butter, 1 ¼ cups granulated sugar, 3 large eggs, room temperature, 1 teaspoon vanilla extract
• Spoon in 1 and 1/2 cups of the orange mixture to the batter and mix until incorporated.   The remaining orange mixture will be used for the glaze.
• Turn the mixer on low and slowly add in 1/3 of the flour mixture to the batter.  Mix until just incorporated.  Next add 1/2 of the buttermilk, again mixing until incorporated.  Repeat adding 1/3 of the flour, then buttermilk, ending with the remaining flour.  
  ¾ cup buttermilk
• Pour the batter into the prepared bundt pan. Smooth out the top with a spatula.
• Bake the cake for 55 to 60 minutes, or until the cake has risen and is firm to the touch, and a skewer (or knife) inserted into the center comes out mostly clean.
• Let the cake cool in the pan set on a wire rack for 10 minutes.  Then, carefully invert the cake onto the wire rack and cool completely.

Orange Glaze

• In a small saucepan, heat the water and remaining processed orange until just simmering.  Cool slightly. 
  ¾ cup water, remaining processed orange
• Transfer the orange mixture to a small mixing bowl. Sprinkle the powdered sugar over the top and mix until smooth. Add more powdered sugar (or water) to reach your desired glaze consistency.
  1 ½ cups powdered sugar
• Generously spoon the glaze over the cooled cake.  Keep any excess glaze to spoon over individual servings for a little more sweetness!
• The cake can be stored covered in an airtight container at room temperature for 3 to 5 days.