Preparation

• Position a rack in the center of the oven and heat to 350°F. Line two large rimmed baking sheets with parchment. Gently spread the streusel on one of the baking sheets and bake, rotating the pan halfway through, until golden brown and fragrant, 12 to 15 minutes. Let the streusel cool to room temperature in the pan on a wire rack before using. (The cooled baked streusel can be stored in an airtight container at room temperature for up to 5 days). Leave the oven at 350°F.
• In a large mixing bowl, whisk the oats, flour, salt, baking powder, and baking soda.
• In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, sugars, and vanilla on medium speed until smooth and creamy, about 2 minutes, scraping down the sides of the bowl as necessary. Add the eggs one at a time, beating until combined and scraping down the bowl before adding the next. Add the dry ingredients in three additions, beating between each addition and scraping down the bowl as needed. Using a wooden spoon or large flexible spatula, fold in the chocolate chips and the streusel.
• Drop the dough by rounded tablespoons onto the prepared baking sheets, leaving 2 inches between each. Bake one sheet at a time for 12 to 14 minutes, rotating the pan halfway through, until the cookies are cracked and golden brown around the edges.
• Transfer the baking sheet to a wire rack, and let rest 10 minutes before removing the cookies to a cooling rack. Store in an airtight container for up to 3 days.