Cream softened butter in a bowl, then add sugar and mix until the texture becomes smoother. Gradually add beaten egg in two parts and mix thoroughly.

Sift dry ingredients into the mixture and fold gently with a spatula until combined. Wrap the dough in plastic wrap and refrigerate for 30 minutes.

Prepare the filling by mixing all filling ingredients together in a bowl.

Roll the chilled dough into a rectangle about 0.5cm thick. Brush melted butter over the surface, leaving a small border around the edges. Spread the filling evenly over the buttered dough.

Roll the dough tightly from one edge to form a log. Seal the edges and wrap in parchment paper. Freeze for at least 1 hour.

Slice the log into pieces about 0.8cm thick. Arrange on a baking sheet with some space between each piece.