Preheat oven to 300 degrees F. Grease a 6-cup bundt pan with cooking spray. Set aside. In a medium bowl, mix together the all-purpose flour, salt and baking powder. Set aside.
To the bowl of a stand-up mixer with the paddle attachment (you can also do this in a medium bowl with an electric hand mixer), add the softened butter, sugar and blood orange zest; beat for about 5 minutes, until pale in color. Mix in one egg at a time, being sure each egg is incorporated before adding another. Turn mixer to high and beat for 2 to 3 minutes, until light and fluffy. Add the vanilla extract and mix.
Fold flour mixture into butter mixture, alternating with the milk, beginning and ending with the flour. Pour the pound cake batter into the prepared bundt pan and transfer to the oven to bake for 45 to 50 minutes, until a skewer inserted into the center comes out clean. Allow the cake to cool for 5 minutes in the pan and then invert onto a cooling rack.