Preheat oven to 425 degrees F.
Spray three 6-cavity doughnut pans (OR two 4-cavity jumbo doughnut pans ) with non-stick cooking spray or wipe with vegetable oil.
Add melted butter, vegetable oil, and granulated sugar to large mixing bowl. Whisk until well combined.
Add eggs, vanilla bean paste, fresh lemon zest and buttermilk. Whisk until well combined. Set aside.
Add all-purpose flour, baking powder, baking soda, and fine sea salt to small bowl. Whisk to combine.
Add flour mixture to sugar mixture. Fold in with large spatula.
Add fresh blueberries to doughnut batter. Fold in with large spatula.
Spoon or pipe blueberry batter into doughnut pans.
Bake regular size doughnuts for 7 to 8 minutes. Bake jumbo size doughnuts 10 to 12 minutes. Doughnuts should be firm to the touch.
Cool in pans for several minutes. Remove doughnuts from pans and cool completely on wire rack.