Preheat the oven to 350 degrees F.
Blend the butter and the granulated sugar in a medium mixing bowl. Add the lemon juice and the egg and continue to blend.
In another bowl, combine the flour, salt and baking powder together.
Slowly add the dry ingredients to the wet ingredients and mix well. Pour in the slivered almonds and gently stir.
Roll the dough into 1-inch balls and place them on a lightly greased or parchment-lined baking sheet.
Bake the cookies for 12-15 minutes (only until the bottoms are lightly browned). Remove them from the oven and cool on a pan for a few minutes.
Pour the confectioners sugar into a large ziplock bag and gently add the cookies. Seal the bag and shake the cookies in the sugar a couple of times. Remove the cookies from the bag and place them on a wire rack. Allow the cookies to cool completely and coat them with the confectioners sugar again.