Preheat the oven to 350 F.  Butter a 9x13-inch cookie sheet or jelly roll pan and line it with parchment paper.

Whisk together the flour, baking soda, pumpkin pie spice, nutmeg, and salt in a medium bowl until blended.

Whisk together the sugar, pumpkin puree, room-temperature eggs, and vanilla extract in a large bowl until smooth.

Dump the dry ingredients into the wet ingredients and stir until all the ingredients are well combined.  No lumps of flour should remain.

Spread the batter in the prepared pan, making sure to get the batter into the corners of the pan.  Try to get the surface level.

Bake at 350 F for 12-15 minutes, until a toothpick inserted into the center comes out clean.  Be careful not to overbake, or it will crack when it's rolled up.

While the cake is baking, cut a piece of parchment paper that's just a bit larger than the pan.  Dust it well with icing sugar.

As soon as it comes out of the oven, flip it out onto the sugared parchment paper and peel off the paper from its bottom.  Carefully roll up the cake, using the sugared parchment paper to help.

Place the rolled-up cake on a wire cooling rack and let it cool completely, about 2 hours.  Do not unroll until it's completely cooled.

Beat the softened cream cheese and butter with an electric mixer until smooth.

Sift the icing sugar into the cream cheese mixture and beat on low speed until combined.  Scrape the sides of the bowl with a spatula and beat on medium-high speed until smooth and fluffy.

If the icing is too soft, add additional icing sugar.  If it's too firm, add a little milk to thin it.  Make sure that the icing is fairly stiff, but still spreadable.

Gently unroll the pumpkin cake.  Spread the cream cheese icing on top, leaving a ½ inch border of cake around the edges to give the icing room to spread as it is rolled.  You may have a little extra icing.

Start at the curled-up end, slowly and tightly rolling the cake.  Use the parchment paper to smooth the log.  Be careful not to squeeze too hard, or the icing will ooze out of the ends.

Place on a cookie sheet or serving plate and chill in the fridge for at least 1 hour.  This allows the icing to firm up, making it much easier to slice.

Trim off the ends to neaten up the appearance.  (Feel free to eat these!)  Serve in 1-inch slices.  Refrigerate any leftovers.