Preheat oven to 350 F. Grease and flour 2 8-inch cake rounds. Set aside.
In a medium bowl, whisk flour, baking powder, and salt together. This is the dry mixture.
In a measuring cup, stir together maple syrup and milk. This is the maple mixture.
In the bowl of a stand mixer fitted with a paddle attachment, mix butter and sugar until light and fluffy.
While the machine is at low speed, add eggs one at a time, beating well after each addition.
Add vanilla and mix until combined. Scrape down the sides of the bowl.
Alternatively add dry mixture and maple mixture, beginning and ending with flour. After all the flour is poured in, mix well until everything is combined.
Bake for 30-35 minutes or until a toothpick inserted in the center comes out with little to no crumbs.
Let cakes cool in the pan for 10 minutes, then invert on to a wire rack to cool completely.
7-minute Frosting
In the bowl of a stand mixer, whisk together egg whites, sugar, cream of tartar, salt and water.
Make a double boiler by putting a stand mixer bowl over a pot of simmering water. Whisk the mixture until it is very warm and foamy.
Remove the bowl from the pot and beat with the mixer until frosting is stiff peak and cooled. This will take about 5-7 minutes.
Mix in the vanilla and beat again. If you want to color the frosting, you can add in gel food coloring and mix again.