Using peeler, peel orange without any white pith; slice peels into slivers or threads then slice into 1-2 centimeter lengths
Set aside in small bowl
Toast whole almonds, watching very carefully and stirring constantly until fragrant and starting to brown
Set aside in bowl
Pre-heat oven to 350F
Place butter in large bowl, adding 1 cup sugar, and baking powder; mix at medium speed until thick and frothy and sugar is completely dissolved
Whisk in eggs, egg yolk, and vanilla extract
Sift salt and flour into large bowl over wet ingredients; add almonds and orange peel and fold ingredients together by hand with wooden spoon until completely combined (the mixture will be very thick)
Weigh dough mass; divide by 4 and portion into 4 equal pieces; shape into 4 loaf-like logs (each weighs about 340 grams)
Place each log onto parchment paper covered cookie sheet; gently flatten with palm
Optional: whisk water and egg white; brush each loaf with mixture and sprinkle tops of loaves with 2 tablespoons of regular or course sugar (we preferred it without sugar)
Bake at 350F for 20 minutes; watch that they don’t brown too much as they will be baked again.
Remove from oven; do not remove from cookie sheets until completely cooled as loaves are very delicate at this stage and will break
Adjust oven temperature to 325F
Once completely cooled, carefully place on cutting board and cut into ½ inch slices with a very sharp knife
Place slices on cookie sheet standing up, not laid on side; bake at 325 F for 7 minutes, turn sheets around in oven and bake 7 more minutes, ensuring cookies do not brown further*
Remove to a wire rack to cool
Weigh butter, sugar and baking powder into TM bowl; cream together for 5 minutes at speed 4 until thick and frothy and sugar is completely dissolved
Add vanilla, salt, eggs and yolk to TM bowl; whisk together for 30 seconds at speed 4
Remove ingredients from TM bowl into large bowl; continue as per #4 above
*every oven is different; 8-9 minutes of baking before turning sheet may be required