Preheat the oven to 450˚F. Butter or lightly spray a baking pan with high sides and set aside.
In a medium bowl, cream together the butter and brown sugar until creamy. Set aside.
In a separate bowl, mix together the flour, white sugar, baking powder and salt until fully combined. Add in the shortening, and using a pastry blender or two knives (or a food processor), mix in the shortening with the flour mixture until the mixture looks like coarse crumbs. Mix in the milk to make the dough.
Turn the dough onto a floured surface, and knead gently around 8-10 times. Roll the dough into a 9 inch square.
Spread the brown sugar mixture evenly onto the surface of the dough. Roll the dough as if you were creating a jelly roll. Seal the edges.
Cut the dough into 12 3/4 inch slices and arrange cut side down in the greased pan.
Bake in the preheated oven for 12-15 minutes. Remove and allow to cool.