Grease and flour a 12 x 17 sheet cake pan or jelly roll pan.
Preheat the oven to 350 degrees.
In a bowl, mix together the flour, baking soda and salt. Set aside.
In another bowl, mix together the buttermilk, milk and vanilla. Set aside.
In a mixing bowl, beat together the butter and sugar until fluffy.
Add in the eggs and beat just until combined.
Alternately add in the dry mixture and the liquid mixture. Start and end with the dry mixture. (dry, liquid, dry, liquid, dry) Mix just until combined after each addition.
Spread into pan and bake at 350 degrees for approximately 15-20 minutes. Start checking at 12 or so. Be careful not to over bake or the cake will end up dry. Sheet cakes bake very quickly.
Set on a rack to cool completely before adding frosting.
Brown Sugar Fudge Frosting:
Melt the butter in a saucepan.
Add cocoa, brown sugar and simmer for several minutes. You want the brown sugar to dissolve.
Remove from heat, add vanilla and let cool to almost room temperature.
Pour into mixing bowl, add salt, confectioners sugar and a couple tablespoons of milk. Beat until smooth. Add more milk (possible up to a ¼ cup) if needed to reach desired consistency.
Spread onto cooled cake.
White Chocolate Buttercream:
Melt one cup of white chocolate and let cool to almost room temperature.
Add to one recipe vanilla buttercream. This recipe can be found on the blog.
Notes
If baking in a 13 x 9 inch pan, you may need to bake it a bit longer. Start by adding on another five minutes and then start checking on it. This recipe card may contain affiliate links. As an Amazon Associate, I earn from qualifying purchases.