1. Adjust oven rack to lower-middle position and heat oven to 350℉. Grease two 6-inch cake pans with butter or cooking spray and cover pan bottoms with rounds of parchment paper. Grease parchment rounds, dust cake pans with flour, and tap out excess. Set aside.
2. Beat eggs, milk, vanilla and saffron with fork in small bowl, set aside. Combine flour, sugar, baking powder, and salt in bowl of standing mixer fitted with paddle attachment; mix on lowest speed to blend, about 30 seconds. With mixer running, add butter one piece at a time; mix until butter and flour begin to clump together and look sandy and pebbly, with pieces about the size of peas, 30 to 40 seconds after all butter is added.
3. Add about 2/3 of egg mixture and mix on low speed until incorporated, 5-10 seconds. Increase speed to medium-high and beat until light and fluffy, about 1 minute. Add remaining egg mixture in slow steady stream, about 30 seconds. Stop mixer and thoroughly scrape sides and bottom of bowl. Beat on medium-high until thoroughly combined, about 20-30 seconds.
4. Divide batter equally between prepared cake pans; spread to sides of pan and smooth with small off-set spatula. Bake until cake tops are light golden and skewer inserted in center comes out clean, 20-22 minutes. Cool on rack 10 minutes. Run a knife around pan perimeter to loosen. Invert cake onto large plate, peel off parchment, and re-invert onto lightly greased rack. Cool completely before icing.
1. Add sugar, butter and salt in a 12-inch skillet and cook over medium heat until sugar is melted. Add plum wedges, increase heat to medium-high and continue to cook until mixture resembles a chunky jam-like consistency, about 6-8 minutes
2. Remove from heat and stir in cinnamon and rum, cool to room temperature.
1. Add milk, tea bags, cardamom and cinnamon in a small sauce pan and bring to a simmer. remove from heat and let steep for 30-45 minutes, cool to room temperature. Remove tea bags and measure 3/4 cup, set aside.
2. Combine sugar, baking soda, flour, cornstarch, and salt in medium bowl. Slowly whisk in milk mixture until very smooth. Pour mixture into medium saucepan. Cook over medium heat, whisking constantly, until mixture boils and is very thick, 5 to 7 minutes. Transfer milk mixture to clean bowl and cool to room temperature, about 2 hours.
3. In stand mixer fitted with whisk attachment, beat cooled milk mixture and extract on low speed until combined, about 30 seconds. Add butter, 1 piece at a time, and beat until incorporated, about 2 minutes. Increase speed to medium-high and beat until frosting is light and fluffy, about 5 minutes. Refrigerate until firm, about 45 minutes.
1. Adjust the quantity of tea bags base on the strength of your tea.
2. Milk base can be made ahead and refrigerate for up to 2 days.
3. Frosting can be refrigerated in airtight container for 1 week. When ready to use, let stand at room temperature until softened, about 1 hour. Beat with stand mixer on medium-high speed until light and fluffy, about 1 minute.
1. Cut each cake in half horizontally. Place one cake layer on the bottom of cake stand or serving platter, spread approximately 1/3 plum filling over cake layer and top with another layer. Repeat with filling and cake layers until top with the 4th cake layer.
2. Spread or pipe frosting on top and side of cake. Garnish with pistachios. Refrigerate cake for 30 minutes, Serve.