Instructions

for the cake

Adjust oven rack to middle position and heat oven to 350 degrees. Grease two 9-inch round cake pans, line with parchment paper, and grease parchment. Process pretzels in food processor until finely ground, 1 to 2 minutes; set aside.
Whisk milk, egg whites, molasses, and vanilla together in 4-cup liquid measuring cup. Using stand mixer fitted with paddle, mix flour, sugar, baking powder, salt, and pretzels on low speed until combined. Add butter, 1 piece at a time, and mix until only pea-size pieces remain, about 1 minute.
Add half of milk mixture, increase speed to medium-high, and beat until light and fluffy, about 1 minute. Reduce speed to medium-low, add remaining milk mixture, and beat until incorporated, about 30 seconds (batter may look slightly curdled). Give batter final stir by hand. Divide batter evenly between prepared pans and smooth tops with rubber spatula.
Bake until tops of cakes are golden and toothpick inserted in center comes out clean, 25 to 30 minutes, switching and rotating pans halfway through baking. Let cakes cool in pans on wire rack for 10 minutes. Remove cakes from pans, discarding parchment, and let cool completely on rack, about 2 hours.

for the frosting

Melt 12 tablespoons butter in 10-inch skillet over medium-high heat. Continue to cook, swirling skillet and stirring often with rubber spatula, until butter is dark golden brown and has nutty aroma, about 3 minutes longer. Transfer browned butter to small heatproof bowl. Let cool for 30 minutes at room temperature.
Using stand mixer fitted with paddle, beat browned butter, cream, vanilla, salt, and remaining 12 tablespoons butter on medium-high speed until smooth, about 1 minute. Reduce speed to medium-low, slowly add sugar, and beat until incorporated and smooth, about 2 minutes.
Increase speed to medium-high and beat until frosting is light and fluffy, about 5 minutes. Measure out 1¼ cups frosting and set aside. (Frosting can be refrigerated for up to 3 days. Let soften at room temperature, about 2 hours, then rewhip on medium speed until smooth, 2 to 5 minutes.)

for the filling

Measure out ¼ cup dulce de leche and set aside. Using stand mixer fitted with whisk attachment, whip cream and remaining dulce de leche on low speed until combined, about 1 minute. Increase speed to medium-high and whip until stiff peaks form, 2½ to 3 minutes (do not overwhip).
Using long serrated knife, cut horizontal line along sides of each cake layer; following scored line, cut each layer into 2 even layers. Place 1 cake layer on platter. Spread 1 cup filling evenly over top, right to edge of cake. Repeat with 2 more cake layers, pressing lightly to adhere and spreading 1 cup filling evenly over each layer. Top with remaining cake layer. Refrigerate for 45 minutes.
Spread thin layer of remaining frosting over top and sides of cake. Refrigerate until frosting is firm, 30 to 45 minutes. Spread remaining frosting evenly over top and sides of cake. Arrange pretzel sticks upright along bottom of cake.
Fill pastry bag fitted with large closed star tip with reserved 1¼ cups frosting. Pipe 8 rosettes around top edge of cake. Place pretzel twists between rosettes. Microwave reserved ¼ cup dulce de leche in small bowl at 50 percent power for 30 seconds, then transfer to clean pastry bag. Cut ⅛ inch slit in tip of bag. Pipe dulce de leche in circles in center of cake. Serve.