Preheat oven to 375 degrees and grease two 6-inch cake pans well with butter or oil. In the bowl of a stand mixer OR with a large bowl and a handheld mixer, cream oil, yogurt, and sugars until light and fluffy, about 2-3 minutes. Blend in pumpkin puree, then add eggs one at a time and beat until incorporated. In a second bowl, sift flour, salt, baking powder, and spices until well combined. In three batches, add flour mixture to wet ingredients, beating until everything is fully mixed. At this point, you may need to add a bit of milk if the batter is too thick: you want it to be pourable, but not too wet that it slops around in your bowl. I only needed to blend about a tablespoon in and it was perfect thereafter!
Pour batter into prepared cake pans. Bake for 40-45 minutes until a toothpick inserted into the center comes out clean. Remove from oven and cool in the pans for 15 minutes, then turn onto a wire rack and cool completely, about an hour.
At this point, I placed the finished cakes in an airtight bag and kept them unfrosted overnight, but you may wish to frost the same day. In either case, start by, with a sharp serrated knife, cutting the domed tops off of the cakes to create a smooth work surface. I saved the scraps and made little cake balls out of them, but you might choose to just snarf up the crumbs. It's quite scrumptious so I wouldn't blame you!
To make the buttercream, beat in your stand mixer or with a hand mixer the butter, sugar, molasses, and spices until a soft but not drippy texture is achieved. I added just a splash of milk to get it smooth and spreadable - think similar to cream cheese.
To assemble the cake, spread buttercream on the cut side of one layer and stack the second atop, again with the cut side facing skyward. Scoop more buttercream on top and frost down the length of the cake, using whatever strokes float your boat. I'm not here to give a frosting tutorial because I am not a professional by any means, but I more or less added frosting and swirled it around until the whole shebang was covered thoroughly. Top with cranberries and a cinnamon stick, if desired. Cover the cake and refrigerate until serving time, with then you can either slice it like a civilized member of society or go caveman and have at it with a fork and knife. Either way, enjoy!