For the filling: Combine all ingredients and beat until smooth. Set aside.
For the glaze: Stir together all ingredients and set aside.
For the bread: Cream together butter and 1/2 cup sugar until fluffy.
Add salt and vanilla. Add egg yolks (remember to save egg whites!) one at a time and beat until creamy.
In a separate bowl, combine 1 1/2 cups flour and baking powder.
Alternate adding dry ingredients and milk to the wet ingredients. Mix until just combined.
In a small bowl, toss blueberries with 1 tbsp. flour. Add them to the bread batter.
In another bowl, beat egg whites until soft peaks form. Add 1/4 cup sugar a tablespoon at a time until stiff peaks form. I used my stand mixer to do this for me while I was preparing the rest of the stuff. Fold into batter.
Pour a little less than half the batter into a greased, floured bread pan.
Then pour the filling over the top of the batter.
Finish off with the remainder batter. Pour glaze on top.