Cream butter and sugar using an electric mixer (about 5 minutes).
Beat in vanilla sugar, eggs (one at a time), salt and orange zest; mix well.
Add milk and mix well.
Add flour and mix until fully incorporated, no clumps left. You should get a batter that is not too thick or watery. If you think it’s too thick add some orange juice until you’re happy with the texture.
Add chocolate flakes/chips and gently stir with the tail of a tablespoon.
Preheat the oven at 350 F
Pour the mixture in the bundt cake molds. Place the molds in a large baking sheet.
Transfer to the oven and bake on medium heat in the middle of your oven for about 30 min or until the cakes are golden (test with a toothpick to see if they’re done. If no batter sticks to the toothpick, then the cakes are done. Don’t open the oven on the first 10 minutes.
Immediately transfer the cakes to a working surface, bottoms up. Leave to cool and meanwhile make the glaze.