With an electric mixer, beat butter, sugar and orange zest in a large bowl.
Add egg and continue beating.
In another bowl, stir together flour, baking powder and salt.
Stir flour mixture and milk alternately into butter mixture.
Stir until mixture is no longer lumpy.
Pour batter in pan and bake for 35 minutes or until a toothpick inserted in the widest part of the cake comes out clean.
Let cake cool completely before removing from pan.
For glaze:
Mix all ingredients in a bowl and drizzle glaze on top of the cake.
Notes
To grease pan:
Start by melting some butter and, with a pastry brush, brush the bundt cake pan, making sure to get into the details of the pan.
Now it's time to coat with flour. Add about 1/4 cup of flour and sprinkle it in the pan and start shaking and turning the bundt pan, so that the flour coats the insides of the pan, including all details.
Turn the pan around and start shaking and patting it gently on the bottom and on the sides to remove the excess flour. You could also cover the bundt pan with plastic wrap and shake to coat. Then invert the bundt pan and dump the excess flour onto the plastic wrap before discarding.