1cup(6 ounces / 170 g) bittersweet chocolate, coarsely chopped, plus more for garnish(or chocolate chips)
flaky salt, for sprinkling
Position a rack in the center of the oven and preheat to 375ºF. Line an 8x8-inch baking pan with parchment on the bottom and sides.
In a large bowl, whisk together the egg and sugar. Whisk in the melted butter or oil and vanilla.
Sift in the flours, baking powder, and fine salt and stir until just combined.
Stir in the chocolate and nuts (if using).
Spread the batter in the prepared pan and top with more hazelnuts, chocolate, and a few pinches of flaky salt. It will seem like not enough batter, but it will puff up as it bakes.
Bake until a toothpick inserted near the center comes out with moist crumbs, 18-22 min. Take care not to overbake.
Cool until warm or room temperature. Slice into bars and devour!
Do-Ahead: Measure out and sift together the dry ingredients. Chop the chocolate. Toast the nuts if using.Storage: These blondies are best when fresh from the oven, but they keep for several days, airtight, at room temperature. You can double-wrap and freeze blondies for up to a month or two; refresh them in a warm oven before enjoying.More Blondies: Double the recipe and bake the batter in a 9x12-inch pan. VARIATIONSChocolate Hazelnut Blondies: For a Nutella vibe, as shown here, use toasted hazelnut oil and toasted hazelnuts. White Chocolate Blondies: Swap the dark chocolate for good-quality white chocolate.Triple Chocolate Blondies: Use 2 ounces each dark, milk, and white chocolate. Peanut Butter Cup Blondies: Use roasted peanut oil in the blondies and chopped up dark chocolate peanut butter cups in place of the chocolate chunks. Brown Butter Blondies: Brown the butter with vanilla bean before adding it to the batter.Nutrition facts are for 1 of 12 servings.