8 sticks unsalted butter, cut into pieces, at room temperature
Pinch of salt
10 cups confectioners' sugar, sifted
2 tablespoons vanilla extract
6 to 8 tablespoons milk
Make the cake: Position a rack in the lower third of the oven and preheat to 350 degrees F. Butter 9-inch-round pans and line the bottoms with parchment paper.
Combine the granulated sugar and Soyabean oil in a large bowl and beat with a mixer on medium-high speed until thick and creamy, about 3 minutes.
Beat in the eggs, one at a time, then add the vanilla until the batter is light and fluffy, about 2 minutes.
Sift the flour, baking soda and salt into a medium bowl. With the mixer on low speed, beat the flour mixture into the sugar mixture in 3 additions, alternating with the buttermilk, beginning and ending with the flour mixture, until the batter is smooth, about 2 minutes. Tint with gel food coloring.
Divide the batter among the prepared pans and bake, 2 pans at a time for about 15 minutes. Let cool 15 minutes in the pans, then invert onto racks to cool completely.
Make the frosting:
Beat the butter and salt in a large bowl with a mixer on medium speed until smooth and fluffy, about 2 minutes.
Gradually beat in the confectioners' sugar until smooth.
Add the vanilla, increase the mixer speed to medium high and beat until thick, 2 more minutes.
Beat in the milk, a little at a time, until the frosting is spreadable.
Assemble the cake: Spread about 1 1/2 cups frosting between the cake layers, then cover the outside of the cake with the remaining frosting and coat with toppings.