Preparation

• Heat the oven to 350°F. Coat the bottom and sides of a 9-by-13-by-2-inch baking sheet with nonstick baking spray.
• Sift together the flour, baking powder, and salt into a medium bowl. Set aside.
• In the bowl of a stand mixer fitted with the paddle attachment (or in a large bowl, using a handheld mixer), cream the butter and brown sugar on medium speed until light and fluffy, about 4 minutes. Add the vanilla paste and beat for 30 seconds. Add the eggs one at a time, mixing thoroughly after each addition. Add the dry ingredients 1/2 cup at a time, beating well after each addition. Scrape down the bottom and sides of the bowl. Add the chocolate chips and beat until evenly distributed, about 1 minute.
• Spread the batter into the prepared baking sheet. Sprinkle the chopped peanuts and fleur de sel over the top. Bake for 45 to 55 minutes, until the edges appear crisp and the top is slightly golden. A toothpick inserted in the center should come out with a few moist crumbs clinging to it. Let the blondies cool completely in the pan on a cooling rack before cutting with a sharp knife.

Make Ahead Tips

Once cooled, the blondies can be stored in an airtight container for up to 4 days; or leave the blondies, uncut, in the pan, wrap in a double layer of plastic wrap, and freeze for up to 2 months.