For the cake: Preheat the oven to 350 degrees F. Generously grease and dust four 9-inch round cake pans with cocoa.
In a mixing bowl, combine the flour, granulated sugar and salt.
In a saucepan, melt the butter. Add the cocoa. Stir together. Add the boiling water, allow the mixture to boil for 30 seconds and then turn off the heat. Pour over the flour mixture and stir lightly to cool.
Combine the buttermilk, baking soda, vanilla and beaten eggs. Stir the buttermilk mixture into the butter/chocolate mixture. Divide the batter among the prepared cake pans and bake for 20 minutes. Cool completely on racks.
For the filling: Halve the strawberries, and then combine them in a bowl with the granulated sugar and vanilla. Mix them all together. Leave them to macerate for 15 minutes, and then drain off the excess liquid.
Whip together the powdered sugar and cream and set aside.
Spread the top of each cake with hazelnut chocolate spread, some whipped cream and strawberries and layer the cakes. Don't assemble more than an hour before serving.