Name: Vanilla Buttermilk Sheet Cake
Prep time: PT-475994H46M45S
Cook time: 20 min
Total time: 1 h 50 min
Cuisine: American
Ingredients: 2 sticks unsalted butter (1 cup / 8 oz); 1 cup water; 2 eggs; 2/3 cup buttermilk; 1 TB vanilla; 2 1/2 cups all-purpose flour (300 g); 2 cups sugar (400 g); 1 1/2 tsp baking soda; 1/2 tsp fine-grain salt (like table or sea salt); 2 cups powdered sugar (240 g); 4 TB unsalted butter (2 oz); 1/4 cup light brown sugar (2 oz / 57 g); 3 TB whole milk; 1/2 tsp vanilla; 1/4 tsp fine-grain salt (like table or sea salt)

Ingredients

Scale

For the cake:

2 sticks unsalted butter (1 cup / 8 oz)
1 cup water
2 eggs
2/3 cup buttermilk
1 TB vanilla
2 1/2 cups all-purpose flour (300 g)
2 cups sugar (400 g)
1 1/2 tsp baking soda
1/2 tsp fine-grain salt (like table or sea salt)

For the frosting:

2 cups powdered sugar (240 g)
4 TB unsalted butter (2 oz)
1/4 cup light brown sugar (2 oz / 57 g)
3 TB whole milk
1/2 tsp vanilla
1/4 tsp fine-grain salt (like table or sea salt)

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Instructions

Preheat oven to 350F

Butter and flour a 10 x 15 x 1-inch jelly roll pan

For the cake:

In a small saucepan, melt the 2 sticks of butter. Remove from heat and let cool for 5 minutes. Whisk in the water.
In a small bowl, whisk together the eggs, buttermilk and vanilla. Set aside.
In the bowl of a stand mixer, sift in the flour, sugar, baking soda and salt. Add the butter-water mixture. Using the paddle attachment, blend on medium-low speed for about 30 - 45 seconds. Add the buttermilk mixture; resume the same speed and blend just until smooth (about 30 - 45 seconds more).
Pour the batter into the prepared pan and bake for 20 - 22 minutes, or until the cake springs back slightly when lightly touched in the center and the sides begin to contract from the pan (the toothpick test is a good indicator, as well). Let cool on a wire rack, while still in its pan, for 15 minutes. Then glaze the warm cake with the frosting. Let the iced cake cool completely and the frosting set before serving, about 1 hour.

For the frosting:

Place the powdered sugar in a medium bowl. Set aside.
In a small saucepan over medium-high heat, bring the butter and brown sugar to a boil, stirring, until the brown sugar is fully dissolved, about 2 minutes. Remove from heat and let cool for about 2 minutes, then whisk in the milk, vanilla and salt.
Pour the butter mixture over the powdered sugar and whisk until completely smooth. Immediately pour over the cooled cake, still in its pan, and spread evenly.

Notes

This is the jelly roll pan I use.
As with most baking recipes, it helps to have all your ingredients at room temperature before starting.
If you have a 2-cup measuring cup, measure the buttermilk in there. Then whisk in the eggs and vanilla - saving you an extra bowl to clean up.
Don't be alarmed, this is a very loose, soupy batter.
For a super smooth frosting, first sift the powered sugar. Although, truthfully, I usually skip this step. Just be sure there aren't any huge clumps.
This frosting sets pretty quickly, so when evenly spreading over the cake, try to work as fast as you can. Nothing "bad" happens if you don't, the frosting just won't have as perfect of a sheen - if that's what you're going for. An offset spatula is handy here, if you have one.