Step 1

Preheat oven to 350°F (177°C). Line large cookie sheets with parchment paper or silicone baking mats (always recommended for cookies). Set aside.

Step 2

Whisk the flour, cream of tartar, baking soda, cinnamon, and salt together in a medium bowl.

Step 3

In a large bowl using a hand mixer or stand mixer fitted with a paddle attachment, beat the butter and granulated sugar together on high speed until smooth and creamy, about 2 minutes. Add the egg, egg yolk, and vanilla extract. Beat on medium-high speed until combined. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. With the mixer running on low speed, slowly add the dry ingredients to the wet ingredients in 3 different parts. The dough will be thick.

Step 4

Roll cookie dough into balls, about 1 heaping Tablespoon (30-35g) of cookie dough each. I recommend this cookie scoop.

Step 5

Mix the sugar and cinnamon together. Roll the dough balls in cinnamon-sugar topping. Arrange cookie dough balls 3 inches apart on the baking sheets. Gently press 5 sliced almonds onto the tops of each dough ball, as pictured above. The almonds may not stick because of the cinnamon sugar, so stick the pointy ends into the cookie dough balls to help them adhere. Again, see the photo above if you need a visual.

Step 6

Bake cookies for 11-12 minutes, or until the edges appear set. The cookies will be very puffy and soft.

Step 7

Allow cookies to cool on the baking sheet for 10 minutes before transferring to a wire rack to cool completely. Cookies slightly deflate as they cool.

Step 8

Cover leftover cookies tightly and store at room temperature for up to 1 week.