Heat the oven to 350°F.
Grease a 9x5-inch loaf pan.
Line the loaf pan with parchment paper, letting two sides hang over the pan.
Whisk the flour, baking powder, baking soda, and salt in a medium bowl.
In a large bowl, whisk the melted butter and sugar until smooth.
Add the eggs, sour cream, milk, vanilla extract, orange zest, and orange juice.
Stir the wet ingredients until combined.
Add the dry ingredients to the wet ingredients.
Stir gently until only a few flour streaks remain.
Place the chopped rhubarb in a small bowl.
Toss the rhubarb with 1 tablespoon flour.
Fold the rhubarb and 3/4 cup white chocolate chips into the batter.
Spread the batter into the prepared loaf pan.
Sprinkle 2 tablespoons white chocolate chips over the top.
Bake for 55 to 65 minutes.
Check the loaf with a toothpick near the center.
The toothpick should come out with moist crumbs, not wet batter.
Tent the loaf loosely with foil if the top browns too fast.
Cool the bread in the pan for 15 minutes.
Lift the bread out of the pan using the parchment paper.
Cool the bread fully before slicing.
For the optional glaze, mix the powdered sugar with orange juice until smooth.
Drizzle the glaze over the cooled loaf.
Let the glaze set before slicing.