3/4 cup egg whites (8-9 eggs)
1 1/2 cups granulated white sugar
1 1/2 pounds almond paste
1/8 cup Meyer lemon juice
Powdered sugar (optional)
Put egg whites and sugar in top of a double boiler or bowl set over a pot of simmering water. Whisk occasionally, until sugar dissolves and mixture is hot but not boiling, about 15 minutes.
Transfer mixture to a mixing bowl. Beat at medium speed with an electric mixer for 5 minutes, then at high speed for 2 more minutes. On low speed, add the almond paste in tablespoon-size chunks until completely incorporated (about 10 more minutes). Add lemon juice to taste.
Transfer mixture to a pastry bag.
Pipe 3 inch circles onto baking sheets lined with parchment paper. Let dry at least 24 hours, uncovered at cool temperature or in the refrigerator.
When ready to bake, preheat the oven to 325°. Remove macaroons from baking sheet and shower with powder sugar and return the cookies to the baking sheet. With your thumb and forefinger, gently squeeze the perimeter of each macaroon to break the dry skin in a few places so the cookie can expand while baking. Bake 20-25 minutes, or until the edges are golden.
Remove to a rack and let cool.