Preheat the oven to 325 degrees. Sift together the flour, baking powder and salt and set aside. Cream together the butter and the sugar. Add the egg and the almond extract and then mix until light and fluffy. Slowly add the flour mixture to the butter mixture. Mix until combined.
Press the dough into the bottom of a well-greased 9x13 pan. For this recipe, I actually grease with butter instead of Baker's Joy. Press with your fingers or a pastry roller to smooth the top of the dough. Using a pastry brush, brush a tiny bit of milk across the top of the dough. Sprinkle with sliced almonds and very lightly press them into the top of the dough.
Bake for 18-20 min, or until just barely beginning to brown around the edges. Do not let them actually brown at all. If they brown, they will be much more crunchy than desired, once they cool. The goal is a very soft shortbread texture.
Let them cool in the pan for 5 minutes and then cut into bars. If they are too soft to cut, let them cool for a few more minutes. Remove them carefully (they will be quite soft) to a wire rack to cool completely before icing. Resist the urge to eat them now. They are even better when they are iced.
Prepare the icing, adding just a tiny bit of milk at a time. If the consistency is too thick, it won't drizzle nicely over the bars. If it is too thin, the icing will just melt into the bars. If you are unsure, test a bit of it on the edge of one bar before drizzling the icing over the entire batch.