Step 1: Prepare the Cookie Dough

1. In a large mixing bowl, cream together the butter and sugar using an electric mixer on medium speed until light and fluffy, about 2-3 minutes.
2. Beat in the egg and vanilla extract until fully incorporated.
3. Gradually add the sifted flour and salt, mixing on low speed until a smooth dough forms.
4. Transfer the dough to a piping bag fitted with a round tip or a zip-top bag with the corner snipped off.

Step 2: Pipe the Cookies

1. Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
2. Pipe 2-inch-long strips of dough onto the prepared baking sheets, spacing them about 1 inch apart as they will spread slightly during baking.
3. Smooth out any uneven edges with a damp fingertip for uniform shapes.

Step 3: Bake the Cookies

1. Bake in the preheated oven for 12-15 minutes, or until the edges of the cookies are lightly golden.
2. Remove from the oven and allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.

Step 4: Make the Chocolate Filling

1. In a microwave-safe bowl or a heatproof bowl set over simmering water, melt the chocolate chips and heavy cream together, stirring frequently until smooth and glossy.
2. Add any optional flavorings like orange zest or peppermint extract, stirring to combine.
3. Allow the chocolate filling to cool and thicken slightly, about 15-20 minutes.

Step 5: Assemble the Milano Cookies

1. Spread or pipe a thin layer of chocolate filling onto the flat side of one cookie.
2. Gently press a second cookie onto the filling to create a sandwich.
3. Repeat with the remaining cookies and filling.

Step 6: Optional Decoration

1. Drizzle the assembled cookies with melted white chocolate or dip half of each cookie into chocolate for a decorative finish.
2. Allow any decorations to set before serving.