Heat oven to 375ºF with rack in the top third. Cut parchment to fit on the bottom of a 10-by-15-inch jelly roll pan and lightly grease the parchment and sides of pan; set aside. Whisk together 1 cup flour, baking powder, cinnamon, ginger, allspice and salt; set aside.
In a mixer beat the eggs and sugar on high speed until fluffy, 4 min. Sir in the pumpkin puree and lemon juice, then the flour mixture, scraping the bowl to incorporate completely.
Place ¼ cup of the batter in a small bowl and stir in molasses and the 3 tbsp flour. Transfer to a piping bag fitted with a #3 plain tip. Pipe swirl designs onto the parchment in the pan. Freeze until solid, about 20 min. Spread remaining pumpkin batter over frozen designs, smoothing the surface. Work quickly so the swirls don’t get warm.
Bake until cake springs back when touched, 16 to 17 min. Run a knife around the edges and turn cake onto a wire rack. Gently remove parchment, then turn cake onto a tea towel, design side facing down. Dust the top of the cake with extra flour to prevent sticking. Starting at the short end, roll the cake to form a log, wrapping with the towel as you roll. Allow to cool in the towel.
Make the filling
In a mixer beat together the cream cheese and butter until smooth. Add the vanilla and confectioners’ sugar and mix. Gently stir in toffee bits and pecans. In a separate bowl whip the cream until firm peaks form. Fold cream cheese frosting into the whipped cream until completely mixed.
Gently unroll cooled cake, remove from towel and spread with filling. Re-roll and place seam-side down on a serving platter. Cover with plastic wrap and chill 1 hr or until ready to serve.
Tip: Let’s talk about the most important thing you should remember when making this cake. When you turn it out and roll it in the towel, the design should be facing down on the towel! This ensures the swirls show up on the outside of the cake when you serve it.