Combine dry ingredients in a medium sized bowl. Cut the butter with a pastry cutter to make a coarse meal. In a small measuring pitcher combine the sour cream, whole egg, egg yolk, extract, and enough milk to make 3/4 cup total liquid ingredients.
Add the liquid ingredients to the dry ingredients and mix with a rubber spatula or wooden spoon until blended. Turn dough onto floured surface and knead slightly five or six times.
For wedges: divide the dough into two equal sized balls. PAt each ball into 6 inch circles, slightly domed in shape. Cut into 8 wedges.
For rounds: roll dough out to 1/2 inch thick and cut into rounds with a floured biscuit cutter.
Place wedges or rounds on an ungreased baking sheet, allowing an inch or more between each scone. Brush with egg white and decorate the tops with sliced almonds. Carefully brush a little more egg white on top to help hold the almonds in place.