Preheat the oven to 350°F. Line two baking sheets with parchment paper.
Bake at 350°F for 9-11 minutes. Sprinkle immediately with flaky salt or fleur de sel. Underbake to preserve a gooey, soft center with crispy edges.
In a large mixing bowl, beat the butter, peanut butter, granulated sugar, and brown sugar until creamy and light, about 2 minutes.
1 cup salted butter, 1 cup creamy peanut butter, 1 cup (200g) granulated sugar, 1 cup (200g) brown sugar
Add the eggs and vanilla extract, mixing to combine. Stop to scrape the bottom and sides of the bowl.
2 large eggs, 1 teaspoon pure vanilla extract
Add the flour, oats, baking soda, and salt. Mix on low speed just until combined but do not overmix. Stir in the chocolate chips and other mix-ins, if using.
1 cup quick oats, 2 1/2 cups (353g) all-purpose flour, 1 1/2 teaspoons baking soda, 1/2 teaspoon salt, 2 cups chocolate chips, 1/2 cup peanut butter chips, Reese's Pieces, Justin's dark chocolate PB cups, plain or peanut M&M's
Use a medium cookie scoop to scoop balls of dough onto the prepared baking sheets, spacing them a couple inches apart.
Bake for 9-11 minutes until just set and starting to turn golden brown around the edges. Remove the cookies from the oven and sprinkle with flaky sea salt. Let cool on the pan for 10-15 minutes before transferring to a wire cooling rack to cool completely.
Flaky sea salt (like Maldon's) or Fleur de Sel