1 ¾ cups/350 grams granulated sugar
½ cup/120 milliliters whole milk
½ cup/115 grams unsalted butter (1 stick)
⅓ cup/30 grams unsweetened cocoa powder
½ teaspoon fine sea salt
3 cups/280 grams quick-cooking oats
⅔ cup/160 milliliters smooth or crunchy peanut butter (not natural)
1 teaspoon vanilla extract
Line two large sheet pans with parchment paper. In a pot, combine the sugar, milk, butter, cocoa powder and salt. Bring ingredients to a rolling boil over medium heat, stirring constantly and being careful not to let the mixture burn, then cook until the cocoa powder and sugar have fully dissolved, about 1 minute. Remove from heat.
Add the oats, peanut butter and vanilla. Stir until well combined, then let cool for about 15 minutes. Drop heaping tablespoonfuls onto the prepared sheet pans, gently pressing the center to flatten slightly. (You should have about 36 cookies.) Chill for a few hours until firm. Store in an airtight container at room temperature for up to 1 week.