In a mixing bowl, cream together ½ cup unsalted butter with ½ cup sugar and optionally 1 teaspoon of vanilla extract. Beat until smooth and light in color, about 3-4 minutes.

In a separate bowl, sift together 2 cups of self-raising flour and 1 cup of cornstarch. Mix well to ensure even distribution. If desired, add 1 tablespoon of fresh aniseed.

Gradually add the dry mixture into the creamy butter mixture, stirring gently until a uniform dough forms. Shape it into a ball, wrap in plastic wrap, and chill for 10 minutes.

Preheat your oven to 350°F (175°C). On a floured surface, roll out the chilled dough to ½ inch thickness. Cut out circles and place them on a baking tray lined with parchment paper.

Bake for about 20 minutes until lightly golden on the edges. Cool on the tray for 5 minutes before transferring to a wire rack.

Spread manjar blanco on the flat side of half the cookies. Top with another cookie to create a sandwich. Dust with powdered sugar before serving.