1 large egg yolk
1/4 cup Thai tea syrup
1 cup unsalted butter, softened
1/2 cup sugar
1/4 teaspoon salt
2 1/2 cups flour
Preheat oven to 375 F degrees. In small bowl, beat yolk and Thai tea syrup with fork until combined; set aside.
In standing mixer, cream butter, sugar, and salt at medium-high speed until light and fluffy, 3 to 4 minutes.
With mixer running at medium speed, add yolk/syrup mixture and beat until incorporated, about 30 seconds.
With mixer running at low speed, gradually beat in flour until combined. Scrape down bowl and give final stir with rubber spatula to ensure that no flour pockets remain.
Using a cookie press, press cookies onto ungreased baking sheets, spacing them about 1-1/2 inches apart. Bake one sheet at a time until cookies are light golden brown, 10 to 12 minutes, rotating baking sheet halfway through baking time.
Cool cookies on baking sheet until just warm, 10 to 15 minutes; using metal spatula, transfer to wire rack and cool to room temperature. Makes about 6 dozen cookies.