Knead almond paste with hands until soft and break into small pieces. Put egg whites with salt in bowl of mixer. Add granulated sugar and almond paste, a little at a time, beating until all is added and mixture is smooth and thick. Beat in powdered sugar, up to 1/2 c if necessary, to make a batter thick enough to hold its shape. Cover baking sheets with 2 layers of heavy brown paper. Drop onto paper by ts into mounds about 2" apart. Bake at 300~ until lightly browned, 20 to 25 minutes. Remove from oven, slide paper off baking sheet onto a damp dish towel folded same size as baking sheet. Let stand until macaroons are cool or can be removed from paper with small metal spatula. Cool on wire racks. Store in tightly covered container.