Preheat your oven to 350 degrees and generously grease a 9 inch loaf pan. Set aside.
In a large bowl, beat together the butter, sugar, eggs, and sour cream until combined. Add in the flour, baking powder, salt, and powdered freeze dried strawberries. Beat until combined- the batter will be very thick. Add in the milk, and beat until smooth.
Pour the batter into your prepared pan and bake for 35-40 minutes, or until a cake tester comes out clean. Cool completely before frosting.
In a small saucepan, cook the flour and milk until a thick paste forms. Stir the mixture constantly while it cooks. Remove from heat and cool completely before continuing.
In a bowl, beat the butter and sugar for 5-10 minutes, until very fluffy and light in color. Beat in the cooled flour mixture and mix for another 5-10 minutes, until the mixture is fluffy. Add in the powdered strawberries and salt, and mix to combine. Frost as desired!