Selai Tetes (Kue Sidik Jari)

Bahan-bahan (28 porsi)

• 225 g (2 sticks) unsalted butter, softened
• 3/4 cup caster sugar / superfine sugar ((regular/granulated sugar ok too, Note 1))
• 2 tsp vanilla extract
• 1 large egg (, at room temperature (~50-55g/2oz))
• 2 1/2 cups plain flour ((all-purpose flour))
• 1/4 tsp cooking salt / kosher salt
• 1/2 cup strawberry or raspberry jam (, or any other flavour, mixed well to loosen (Note 2))