Step 1Heat the oven to 350 degrees. Grease and flour 2 (9-inch) springform pans.
Step 2In a medium bowl, sift together the flour, baking soda, cinnamon, nutmeg, cloves, ginger and salt.
Step 3In a separate large bowl with a fork, stir together the eggs and sour cream. Stir in the brown sugar and then the oil until just combined; be careful not to overwhisk.
Step 4Gently stir the flour mixture into the batter just until incorporated and there are no lumps. Stir in the pumpkin puree.
Step 5Divide the batter between the two prepared pans. Bake the cakes for about 25 to 30 minutes, until golden brown on top and a toothpick inserted in the center comes out clean (the cakes are moist and there may be a few crumbs on the toothpick, but there should be no batter). Remove and allow the cakes to cool, still in the pans, on a wire rack to room temperature.
Step 1Melt the chocolate in a bowl set over a pan of gently simmering water. Remove from heat.
Step 2Gently fold the sour cream into the chocolate until incorporated and uniform in texture, then stir in the salt.
Step 3Remove the cakes from the pans and place one on a cake stand or serving plate with the flat-bottomed side up and spoon one-fourth of the ganache over the cake. Spread the ganache evenly over the top.
Step 4Place the second cake, domed side up, evenly over the first and spoon one-half of the remaining frosting over the cake, evenly covering the top and sides. Add additional frosting as needed to coat the cake evenly.
Step 5Press the pecans into the sides of the cake. The cake can be kept at room temperature for up to 2 days.