Preheat the oven to 375 F.
Whip the butter and icing sugar together in a stand mixer with the whisk attachment for 20-30 minutes.
While the butter and icing sugar are in the mixer, toast the almonds by putting 1 cup of sliced/slivered almonds in a pan over high heat.
Continuously stir the almonds and make sure each side gets golden brown then remove from heat and set aside.
Once the butter and sugar mixture is white, airy, and fluffy, turn the mixer off and remove the whisk attachment.
Add the dough hook or paddle attachment and add the salt, egg and egg yolk, and vanilla and mix until combined.
Add 2 cups of flour, mixing as you go, then add the rest of the flour ½ cup at a time until the dough is soft, but pulls away from the sides of the bowl.
Once the dough is ready, fold in the almonds.
Prepare 2 large baking trays with a sheet of parchment paper and roll the dough into small walnut sized balls and place them 1 inch apart on the baking sheet.
Add a thumbprint to slightly press each ball down.
Sprinkle the pan full of cookies with rosewater, then place them in the oven for 15-20 minutes on the middle rack.
While one sheet is baking, prepare the next sheet by repeating the same steps.
When the cookies are slightly golden brown, remove them from the oven and immediately top them with a heaping pile of icing sugar.
Let them cool, then place them on a platter and enjoy!
