Preheat the oven to 350°F (175°C) and line two baking sheets with parchment paper.
In a large bowl, beat the softened butter and peanut butter together until smooth and creamy, about 1 minute.
Add the brown sugar and granulated sugar and mix until light and fluffy, about 2 minutes.
Beat in the egg and vanilla extract until fully combined.
In a separate bowl, whisk together the flour, baking soda and salt.
Add the dry mixture to the wet ingredients and stir just until no dry flour remains.
Fold in the chocolate chips.
Cover the bowl and refrigerate the dough for 30 minutes.
Scoop the dough into balls of about 1½ tablespoons each and place them 2 inches apart on the prepared sheets.
Gently press each ball down with your palm, or press a fork across the top in a crisscross pattern.
Bake one sheet at a time for 10 to 11 minutes, until the edges are lightly golden and the centers still look slightly soft.
Sprinkle with flaky salt if you like. Let the cookies rest on the sheet for 5 minutes, then move them to a wire rack.
