Pumpkin Cake with Butterscotch Filling and Brown Sugar Icing

Cake:
2 c. all-purpose flour
2 tsp. baking soda
1 tsp. ground cinnamon
1 tsp. ground nutmeg
1/2 tsp. ground cloves
1 tsp. salt
1 1/2 c. pumpkin puree
1 c. buttermilk
2 sticks unsalted butter
1 c. tightly packed light brown sugar
1 c. sugar
4 lg. eggs
1 tsp. vanilla extract

Filling:
3/4 c. heavy cream
3/4 c. sugar
1/4 tsp. fresh lemon juice
1 stick unsalted butter, cut into 4 - 1 oz. pieces
3/4 c. chopped nuts, such as pecans or walnuts (optional)

Icing:
2 c. tightly packed light brown sugar
1 c. heavy cream
2 sticks unsalted butter, cut into 8 - 1 oz. pieces
1/4 tsp. cream of tartar

Line bottoms of two round 9-inch cake pans with parchment paper. Grease parchment, as well as sides of pans. Preheat oven to 325°F. Center a rack in the oven.

To make cake, combine flour, baking soda, spices, and salt in a medium bowl. Set aside. In a small bowl, combine pumpkin puree and buttermilk and mix until smooth. Set aside. In the bowl of an electric mixer fitted with paddle attachment, cream together butter and sugars. Beat on medium speed for 2 minutes. Scrape down sides of bowl. Increase to high speed and beat for an additional 2 minutes. Scrate down sides of bowl. Add eggs one at a time, mixing well, and scraping down sides of bowl between additions. Add vanilla extract and beat on high for 30 seconds. With mixer running on low speed, alternate adding dry and wet ingredients. Mix until just combined. Remove bowl from mixer and use a rubber spatula to finish mixing batter, until smooth and thoroughly combined.

Immediately divide batter between prepared cake pans, spreading evenly. Bake for 45 minutes or until a toothpick inserted in center comes out clean. Allow to cool in pans 10 minutes. Invert onto wire cooling rack and allow to cool completely.

To make filling, heat cream in a saucepan over medium-low heat until hot (do not allow to boil or simmer). Combine sugar and lemon juice in a separate saucepan and stir with a whisk to combine (sugar will resemble moist sand). Caramelize sugar for 4 to 5 minutes over medium-high heat, stirring constantly with a whisk to break up any lumps. Remove saucepan from heat. Add hot cream, one half at a time. Add butter, one piece at a time, stirring to incorporate completely before adding next piece. Cool in refrigerator 45 minutes. Place in the bowl of an electric mixer fitted with paddle attachment and beat on high speed for 2 minutes until light (but not fluffy). Add chopped nuts and stir to incorporate. Set aside.

To make icing, heat brown sugar, heavy cream, 2 - 1 oz. pieces of butter, and cream of tartar in a 2- or 3-quart saucepan over medium-high heat, stirring frequently, while bringing mixture to a boil. Allow mixture to continue boiling while stirring constantly for 2 minutes. Transfer bubbling hot mixture to stainless steel bowl and allow to stand at room temperature for 1 hour before proceeding. Place cooled mixture in the bowl of an electric mixer fitted with paddle attachment. Beat on low speed for 30 seconds. Increase speed to medium and beat for 2 minutes, adding 6 remaining pieces of butter one at a time, until incorporated. Scrape down sides of bowl. Increase speed to high and beat for an additional 2 minutes. Scrape down sides of bowl and beat on high for an additional 1 minute until light and fluffy.

To assemble cake, place one of the pumpkin cake layers on a cake platter or a cardboard cake circle. Spread butterscotch filling evenly on top of cake. Top with remaining layer of cake, pressing down firmly. Frost sides and top of cake with brown sugar icing. Use remaining frosting to pipe decorative accents onto top and bottom edge of cake. Refrigerate for 30 minutes before cutting and serving.