Strawberry filling is a thick fruit paste made to survive baking. Typically it is based on sugar and glucose syrup with strawberry puree, juice concentrate or flavouring, a gelling agent such as pectin, an acid like citric acid for tartness, and colour to keep it bright red after the oven. Some versions also contain apple or other fruit pulp as a base.
Unlike ordinary jam, it is formulated to stay in place when heated, without bubbling over or drying out, and to stay soft inside a crisp biscuit. In Denma filled cookie with fruits, strawberry is one of three fillings, next to prune and apricot, each set into a buttery cookie.
How much real fruit a filling contains varies a lot between brands, and the ingredient list shows whether strawberry or only strawberry flavouring is used. The filling itself is usually free of the major allergens; the cookie around it, here made with wheat flour, butter and egg, is not.
