Preheat the oven to 340°F.
Line three 6-inch round cake tins.
Mix together the milk and vinegar, then set aside to thicken.
Add the remaining wet ingredients to the milk mixture.
Sift in the dry ingredients and mix until combined.
Pour the batter into the tins.
Bake for 25-35 minutes, or until a knife inserted into the center comes out clean and the sponge springs back when touched.
Let the cakes cool before leveling them.
Using a hand mixer or stand mixer with a paddle attachment, cream the butter on medium-high until light and fluffy. With the mixer on low, add the powdered sugar gradually, scraping down the sides of the bowl after each addition. Add in the chocolate hazelnut spread and milk, and mix until well combined.
Heat the cream until it begins to simmer, whisking constantly. Remove from heat and pour over the chocolate hazelnut spread. Let it sit for a couple of minutes before mixing until smooth.
Once everything is cool, assemble the cake with the buttercream, crushed hazelnuts, and ganache.