Let 1 large egg sit at room temperature.

Place 1 ½ sticks unsalted butter in a large microwave-safe bowl and microwave until melted. (Alternatively, melt the butter in a small saucepan on the stovetop, then transfer to a large bowl.)

Add ¾ cup packed light brown sugar, ½ cup honey, 1 ½ teaspoons kosher salt, and 1 teaspoon ground cinnamon, and whisk to combine. The mixture should be just warm at this point (if it feels very hot, leave it to cool for a few minutes before the next step). Add the egg and whisk to combine.

Add 3 ½ cups bleached all-purpose flour, 1 teaspoon baking soda, and ½ teaspoon baking powder, and stir with a large rubber spatula until the flour is fully incorporated with no dry steaks visible. The dough will form a ball and look glossy and slightly sticky.

Divide the dough in half (about 17 ½ ounces each). Wrap each half in plastic wrap and shape into a flat rectangle of even thickness (the exact size doesn’t matter). Refrigerate the dough until firm, at least 1 hour and up to 2 days.

Arrange 2 racks to divide the oven into thirds and heat the oven to 350°F. Roll out one piece of dough at a time (keep the other half in the refrigerator): place the dough between 2 sheets of parchment paper. Roll out to a rectangle that is just under 16x12-inches and 1/16-inch thick.

Transfer the dough, still sandwiched between the parchment paper, to a rimmed baking sheet. Peel away the top layer of parchment. Repeat rolling out the second piece of dough and place on a second rimmed baking sheet.

Bake, rotating the baking sheets from front to back and top to bottom halfway through, until pale golden brown, 10 to 12 minutes total. The layers will be soft with slightly firmer edges and the surface will no longer look wet or shiny. Let the cake cool on the baking sheets for 10 minutes. Transfer, still on the parchment, to wire racks to cool completely.

Reduce the oven temperature to 325°F. When the layers are completely cooled, cut each sheet crosswise into 4 pieces.

Place one of the pieces back on a baking sheet. Return to the oven and bake until deep golden brown, 12 to 15 minutes. Let cool completely on the baking sheet (it will become crisp). Place in a food processor and pulse into fine crumbs. (Alternatively, break the piece into large pieces, then transfer to a large zip-top bag and use a rolling pin to crush into fine crumbs.)

Place 16 ounces sour cream, 1 (13.4-ounce) can dulce de leche, ¼ cup honey, and 1 teaspoon kosher salt in a stand mixer (or large bowl if using an electric hand mixer or whisking by hand). Beat with the whisk attachment on low speed until just combined. Scrape down the sides of the bowl with a rubber spatula. Add 1 quart cold heavy cream and beat on medium-high speed until glossy and fluffy and medium-firm peaks form when the whisk is lifted, 10 to 14 minutes.

Remove the bowl from the mixer. Whisk the mixture briefly by hand to ensure all the cream is evenly whipped.

Place one cake piece on a platter or board that will fit in the refrigerator. Spoon about 1 heaping cup of the filling onto the cake, then spread into an even layer with a small offset spatula, going all the way to the edges. Repeat layering the remaining 6 cake layers and filling, ending with a layer of cream (you should have some cream leftover). As you spread and layer the filling, some will slide down the sides; that’s OK!.

Spread the remaining cream onto the sides of the cake, making sure the entire cake, including the corners, are fully covered. Press the reserved cake crumbs around the bottom edge of the cake.

Refrigerate the cake uncovered overnight so the layers can fully soften. Serve the cake chilled, cut into thin slices.