Preheat & Prep: Preheat oven to 375°F (190°C). Line baking sheets with parchment paper (or use a nonstick pan).
Cream wet ingredients: Beat the softened butter and 1 cup peanut butter until smooth and creamy (1–2 minutes). Add the granulated sugar and light brown sugar; beat until light and fluffy (about 2 minutes).
Add egg & liquids: Beat in the egg, milk, and 2 teaspoons vanilla extract until fully incorporated.
Mix dry ingredients: In a separate bowl, whisk flour, baking soda, and salt. Gradually add to the wet mixture on low speed until just combined.
Optional chill: For even better flavor melding and to keep them extra chewy, chill the dough for 1–2 hours (or overnight).
Shape and roll: Scoop rounded tablespoonfuls of dough and roll into balls. Coat each in granulated sugar. Place 2 inches apart on sheets and lightly press down with the palm of your hand.
Bake: 8–10 minutes, until lightly golden and cracked on top (centers may look slightly soft).
Add Kisses: Right out of the oven, press a kiss into the center of each cookie.
Cool: Let sit on the sheet 3–4 minutes, then transfer to a rack. Chocolate will set as they cool.
Video
Notes
Chilling the dough enhances flavor and prevents spreading.
Be careful not to overbake these cookies or they will become more dry and brittle.