Butter a baking sheet or line it with parchment. In a large bowl, beat the egg yolks with 3/4 cup of the sugar until light and the sugar is dissolved. Stir in the melted butter, almonds, raisins and orange peel. In a separate bowl, beat the egg whites until they just begin to form peaks and gradually beat in the remaining 3/4 cup sugar until the whites form stiff peaks.

Sift the flour and baking powder together. Fold in 1/3 of the flour into the yolks; then fold 1/3 of the egg whites in. Repeat, alternating, until well combined. The dough will be firm and slightly sticky. If the dough is too soft, add more flour. With floured hands, divide the dough into two logs approximately 1 1/2 inches wide. Arrange the logs on the prepared baking sheet and bake for 20 to 25 minutes or until they are lightly brown and firm to the touch. Remove from the oven and set the baking sheet on a rack for 10 minutes. On a cutting board, cut the logs on a diagonal into slices 1/2 inch wide. Return the slices to the baking sheet and bake for 5 to 7 minutes on each side or until the biscotti are very lightly browned and crisp. Cool on racks and store in airtight containers.