For the Pumpkin Layer Cake: Preheat your oven to 350 degrees F and grease or spray with nonstick three 6-inch cake pans.
Place the 6 ounces butter, granulated sugar and muscovado in an electric stand mixer fitted with the paddle attachment and mix on medium until creamy and well blended, about 3-4 minutes. Add in the pumpkin and mix for 1 minute more. With the mixer on low, add the eggs one at a time mixing completely before adding in the next. Add the water and vanilla and run the mixer on low for 1 minute more.
In a medium bowl whisk together the flour, cinnamon, baking powder, baking soda, sea salt, allspice, nutmeg, ginger and cloves. Pour into the stand mixer and mix on low until barely combined and you still see streaks of flour. Take the bowl out of the mixer and gently fold the batter several more times until you see no more streaks. Distribute the batter evenly amongst the three prepared pans (about 2 1/2 cups-ish of batter per pan). Tap each pan on the counter several times to release any trapped bubbles.
Bake the cakes in the center of the oven for 32-35 minutes. I like to lightly press the center of the cakes to see if they're done...if they spring back they are done. If they leave a bit of an indent, they need a bit more time in the oven. Let cool for 30 minutes in the pan, then run a knife around the edge of the cake and gently turn out onto a cooling rack. I like to hold one hand on the top of the cake to help it out. If it resists coming out, let it cool a bit more in the pan. Cool completely before frosting.
For the Clusters: Reduce your oven to 300 degrees F and cover a rimmed baking sheet in parchment paper.
Place the 4 tablespoons of butter in a small saucepan over low heat. Once the butter has melted, turn the heat up to medium and stir and watch until you start to notice little golden bits settling on the bottom of the pan and you smell a nutty, caramel aroma. Immediately transfer to a heat-safe bowl (taking care to get all those yummy golden bits from the bottom of the pan) and whisk in the water and maple syrup and set aside.
Place the flour, brown sugar, granulated sugar, corn starch, cinnamon and sea salt in an electric stand mixer fitted with the paddle attachment and run on low for 1 minute to mix. Drizzle the brown butter mixture over the top, sprinkle in the pepitas and pecans and run the machine on low for several minutes more until it has the consistency of wet sand. Remove the bowl from the mixer and spread across the parchment-covered baking sheet, squeezing to form small clumps. Place on the center rack of the oven and bake for 20 minutes. Let them cool on the baking sheet; they will crisp up as they cool. Once cool, store leftovers in an airtight container in the freezer for later use.
For the Frosting: Place your softened butter and cream cheese in the electric stand mixer fitted with the paddle attachment and run on medium until thoroughly combined. Add in the sugar, cinnamon and nutmeg and run the machine for 2 minutes more or until thick and creamy. Add in the milk to thin a bit. Check the consistency. Add more milk in small, 1 teaspoon bits if it needs to be thinned further.
To Assemble: To frost, set one layer on a cake plate right side up, frost, sprinkle with clusters and place another layer on top. Frost, sprinkle and repeat the remaining layers. Finish by frosting the sides of the cake. Grab some seasonal flowers, rid them of bugs and nature and arrange them along the side of the cake.