vanilla extract
An infusion of vanilla pods in alcohol, liquid and intensely aromatic.
Vanilla extract is a standard baking item in English-speaking countries, while in German-speaking ones it is not always stocked next to vanilla sugar but can be found in the baking aisle of larger supermarkets, health food shops or online. Look for pure extract rather than imitation flavouring made with vanillin.
Substitute:
The seeds of half a vanilla pod replace about a teaspoon of extract and taste rounder; vanilla sugar also works but adds sugar, which should be reduced elsewhere in the recipe.