ream together butter through almond extract until light. 5 min. or more.
Add egg whites one at a time and beat well after each addition.
Stir in flour and milk, alternating between the two, starting and ending with the flour. (i.e. ⅓ flour, ½ milk, ⅓ flour, ½ milk, ⅓ flour)
Pour into pans (2 9-in. round or one 9x13-in) and bake at 350. 25-30 minutes or until done.
Notes
Update: King Arthur has updated the recipe a bit and it is now called Tender White Cake. For a slightly revised version that uses all butter and a different mixing technique, check out King Arthur's site.