Preheat oven to 400 degrees. Make the cakes: Line two 9-by-13-inch rimmed baking sheets with parchment paper, and lightly coat with spray. Beat egg yolks with a mixer on high speed until pale yellow and thick, 4 to 5 minutes. Transfer to a medium bowl.
Beat egg whites in a clean mixer bowl on medium speed until soft peaks form, 1 to 2 minutes. Raise speed to medium-high; slowly add sugar, beating until stiff peaks form. Transfer mixture to a large bowl.
Fold yolks into egg-white mixture using a rubber spatula, being careful not to deflate whites. Sift cocoa and flour over top; gently fold to combine. Pour into prepared sheets, and gently smooth tops using an offset spatula.
Bake until cakes spring back when touched, 9 to 10 minutes. Meanwhile, line 2 wire racks with parchment paper, and lightly coat with spray. Remove cakes from oven, and immediately turn out each onto a prepared rack. Peel parchment from cakes. Let stand until cooled completely.
Assemble the cakes: Place 2 clean kitchen towels on work surface, and transfer each cake (with parchment) to a towel. Divide caramel cream evenly between cakes. Spread, using an offset spatula, leaving 1/2-inch border around edges.
Tightly roll 1 cake into a log, starting with a short end, removing parchment as you work. Tightly wrap log in kitchen towel. Repeat with remaining cake. Transfer wrapped logs, seam side down, to a baking sheet, and refrigerate until firm, at least 2 hours or up to 2 days.
Unwrap each log. Lightly dust work surface with cornstarch or confectioners' sugar. Roll out half the fondant to 1/4-inch thickness. Place an 8-by-12-inch food-safe wood-grain texture mat (available at chineseclayart.com) on fondant, and press hard, using a rolling pin, to make an indentation. Gently remove mat, and generously rub fondant with cocoa. Brush off excess cocoa.
Drape 1 cake log with fondant sheet. Shape fondant to fit log using your hands, and trim ends and cut away excess with a paring knife or a pizza cutter. Transfer to a serving platter. Repeat with remaining fondant, cocoa, and cake log. Serve with sugared white pine needles and milk-chocolate pinecones if desired.