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1
Heat the oven to 350 degrees F and arrange a rack in the middle.
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2
Line a baking sheet with parchment paper and set aside.
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3
Place 1/4 cup of the sugar in a small bowl and set aside.
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4
Combine the butter and the remaining 1 1/4 cups sugar in the bowl of a stand mixer fitted with a paddle attachment and mix on medium speed until light in color and fluffy, about 2 minutes.
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5
Stop the mixer and, using a rubber spatula, scrape down the sides and bottom of the bowl.
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6
Add the yolks, vanilla, and salt and mix on medium speed until smooth, about 30 seconds.
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7
Reduce the speed to low; add the flour, baking soda, and cream of tartar; and mix until the dough just comes together.
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8
Scoop the dough by rounded tablespoons and roll it into balls between your hands until smooth.
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9
Coat in the reserved sugar and place on the prepared baking sheet at least 2 inches apart, for a total of 12.
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10
Bake until golden brown around the edges but still soft in the center, about 15 to 16 minutes.
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11
Immediately transfer the cookies to a wire rack to cool completely.
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12
Repeat with the remaining dough.
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13
Set aside 20 cookies for the sandwiches.
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14
Using a 3-tablespoon or 1-1/2-ounce ice cream scooper and working with 6 cookies at a time (3 bottoms and 3 tops), place a scoop of ice cream on each bottom cookie and top with another cookie.
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15
Firmly press the cookies together to evenly disperse the ice cream in the center (be careful not to break the cookies).
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16
Immediately wrap each sandwich with plastic wrap and place in the freezer.
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17
Repeat with the remaining cookies and ice cream.
