In a bowl, mix flour and salt, set to side
Whip egg whites, cream of tartar, and sugar until stiff
Whisk yolks, paste, milk, oil, coffee paste (coffee+water), then mix in flour, until completely combined
Fold in egg whites in batches, trying not to deflate it as much as you could
Pour batter into greased and floured tube/flute pan, bake on preheated 340F (170C), for 40-45 minutes
Flip pan upside down and let cool for an H. If your pan has feet, easy to flip, if not, let the pan hang in a bottle, upside down
To make buttercream, whip butter, sweetened condensed milk, paste, essence and icing sugar
Cover cake with buttercream