Preheat your oven to 350°F and position the oven rack in the middle. Line two rimless baking sheets with parchment paper. In a bowl, whisk together the flour, baking powder, and salt.
In a medium bowl, whisk the sugar, melted butter, egg, egg yolk, and vanilla until well combined. Gradually stir in the flour mixture until no dry streaks remain. Add the oats, rice Krispies, and chocolate chips, and mix until fully incorporated. The dough will be sticky.
Use a cookie scoop to evenly divide the batter onto the prepared baking sheets, spacing them about 2 inches apart.
Bake the cookies one sheet at a time, for 15 to 17 minutes, rotating the sheet halfway through, until the edges are browned and the middle is light brown and set Be careful not to overbake.
Allow the cookies to cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely. Once cooled, they can be stored in an airtight container for up to 3 days.
Notes
Old-fashioned rolled oats can be used instead of quick oats. Do not use the instant oats that come in the individual serving size.