Sift together flour, cocoa, and salt in large bowl. Set aside.
With stand or hand mixer, cream together coconut oil and sugar for 1-2 minutes. Add eggs one at time and vanilla extract. Beat until creamy, several minutes.
With mixer on low, add dry ingredients and sour cream alternately, starting and ending with dry ingredients. Lastly, add cup of hot water in which you have dissolved 2 teaspoons of baking soda. Mix until combined.
Drop by tablespoon onto lightly greased (or parchement-lined) baking sheet. Bake for about 10 minutes. Cool completely before filling.
Filling
Beat egg whites until stiff. (You know they’re stiff when bowl is inverted and whites do not fall out)
With mixer on, add vanilla, flour, milk, and 2 cups of confectioners’ sugar, scraping down sides of bowl as needed. Cream for 2 minutes. Add butter and remaining 2 cups of confectioners’ sugar and beat until fluffy.
When cakes are completely cool, spoon cream filling onto cakes, covering with other side to make a sandwich.
