Preheat the oven to 350 degrees F. Grease and flour a 18 by 13-inch rimmed baking sheet.
In a large mixing bowl, combine the flour, sugar, baking soda, and salt. In a separate mixing bowl, beat the eggs and mix in the sour cream, and vanilla. Add the egg mixture to the flour mixture, mixing until just combined.
In a saucepan over medium-high heat, melt the butter and stir in the cocoa powder, and hot water. Bring the mixture to a boil and then remove from the heat. Cool slightly, and incorporate the cocoa mixture with the dry ingredients, mixing just until blended.
Pour the batter into the prepared pan. Bake for 25 minutes, or until a tester inserted into the center comes out clean. Cool completely.
For the Frosting:
In a large heavy-bottomed saucepan over medium heat, melt the butter. Add the peanut butter and mix until smooth. Remove from the heat. In a separate large bowl, whisk together the milk, and powdered sugar until fully incorporated. Stir in the vanilla, and slowly incorporate the peanut butter mixture, blending well after each addition.
This frosting is best to spread when warm, so you may need to reheat it when constructing your pinecones.
With an oval cookie cutter, cut ten ovals from the cake (you can also cut ovals freehand with a paring knife). Once you have your ovals, trim each one to resemble a pinecone: create a pointed tip on one end and a rounded base on the other. Then, shave off corners and top with the knife so that each cake further takes on a pinecone shape.
Frost one cake at a time, arranging sliced almonds in the frosting to look like the scales of a pinecone. Start at the base and set the almond slices, pointy end out, in a spiral pattern. Continue adding almond slivers until the entire surface is covered. Repeat until all cakes are frosted and decorated.
To create "snow-covered" pinecones, dust the cakes with powdered sugar and serve.