Chocolate-Hazelnut Swirl Cake

Whisk flour, sugar, and salt in a bowl. Using your hands or a fork, work butter into mixture until texture is crumbly. Stir in hazelnuts.

Preheat oven to 350°F. Coat a 9-by-5-inch loaf pan with cooking spray. Line with parchment paper, leaving a few inches of overhang on long sides. Coat parchment with cooking spray.

Combine flour, baking powder, and salt in a medium bowl. Beat butter and sugar in a large bowl with an electric mixer on high speed until light and fluffy, 3 to 4 minutes. Add eggs, 1 at a time, beating well after each addition. Stir in vanilla.

With mixer on low, add half of flour mixture to butter mixture, then half of milk, beating until just combined. Repeat with remaining flour mixture and milk.

Transfer half of batter to empty flour mixture bowl. Add hazelnut-chocolate spread, cocoa powder, and 1 tablespoon warm water. Stir until combined.

Place 1/4-cup scoops of batter into prepared pan, alternating between chocolate and vanilla. Use a knife to spread each scoop of batter to edges of pan. Gently run knife through batter lengthwise a few times to swirl.

Bake until puffed and top is set, about 40 minutes. Sprinkle with streusel. Continue baking until a toothpick inserted in center comes out clean, 20 to 25 minutes. (Cover with aluminum foil during final 10 minutes to prevent excess browning.) Let cool in pan for 5 minutes, then transfer to a wire rack to cool completely before slicing, about 1 hour.