Prepare Heat the oven to 350°F (175°C) with a rack in the center. Line a cool baking sheet with parchment. In a small bowl, stir together the flour, baking powder, and salt.

Mix the wet ingredients In a medium bowl, whisk the egg yolk, sugar, oil, milk, and vanilla for about 45 seconds, until evenly combined and glossy with no separate ring of oil. The sugar may remain slightly grainy.

Add the dry ingredients and rest Fold in the flour mixture with a spatula until no dry flour remains. Let the dough rest for 10 minutes. A small piece should hold together when gently pressed.

Shape Divide into eight portions, approximately 23 g each. Round gently and arrange at least 2 inches apart. Flatten each portion to about 1¾ inches across and ⅜ inch thick. Divide the optional teaspoon of sugar over the tops.

Bake Bake for approximately 10–12 minutes, checking at 10 minutes. Look for set edges, a surface that no longer looks wet, and light golden color around the rim or underneath. If the center still looks wet, continue baking and check again shortly.

Cool Leave the cookies on the baking sheet for 5 minutes. Transfer carefully to a rack with a thin spatula and cool for at least another 5 minutes. Cool completely before storing.