Preheat oven to 350°F (175°C). Lightly spray a 9x13 inch pan with baking spray, or line with parchment paper. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or a large mixing bowl with a handheld mixer, add the butter. Beat on medium-low speed for 3 minutes or until light. Add sugar and beat on medium speed for 1 minute.
Add eggs one at a time, mixing well after each addition. Add the vanilla, sour cream, milk (or buttermilk), and the food coloring, and mix just until combined.
In a medium mixing bowl, whisk together the flour mixture, baking soda, and salt. With mixing speed on low, gradually add the dry ingredients. Mix on medium for 15 seconds.
Pour the cake batter into the prepared pan. Spread into a smooth, even layer.
Place in the oven and bake for 25-30 minutes or until the top springs back when touched. Remove from the oven and allow to cool for at least 30 minutes before frosting.
To Make the Frosting
In the bowl of a stand mixer fitted with the paddle attachment, or a large mixing bowl with a handheld attachment, add the butter. Beat on medium-high speed for 2 minutes.
With mixing speed on low, gradually add the powdered sugar, cocoa powder, milk, corn syrup, vanilla, and salt.
Carefully bring the speed up to medium-high, and beat for 2 minutes.
Spread over the cooled cake, and decorate as desired.
Notes
I like to add an additional 1 tsp of buttery vanilla emulsion to this recipe.
To STORE Homemade Yellow Cake, cover it tightly and keep it at room temperature in an airtight container for up to 3-5 days. For longer storage, you can FREEZE the cake for up to 3 months by wrapping it in plastic wrap and aluminum foil.To REHEAT, let it thaw at room temperature, then warm individual slices in the microwave for 10-15 seconds.