• In the bowl of a stand mixer fitted with a paddle attachment or a large bowl, add the flour and pinch of salt.
• Mix in the softened butter and knead to bring together a smooth dough.
• Form the dough into a disc, wrap in plastic, and refrigerate for 30 minutes.
• Preheat oven to 350˚F (180˚C). Line two baking sheets with parchment or lightly grease.
• On a very lightly floured surface or between two sheets of parchment paper, roll the refrigerated dough into a sheet about 1/4 inch (6 millimeters) thick. If the dough is falling apart, bring it together and knead lightly before rolling again.
• Use a 1 1/2-2 inch (4-5 centimeter) round cutter to cut out circles in the dough. Gently transfer to the prepared baking sheet at least 1 inch (2.5 centimeters) apart. If the dough is sticking to the surface, use a very thin offset spatula to carefully remove without pressing the dough. Bring together the scraps of dough, roll out again, and cut to make additional cookies.
• Bake in the preheated oven just until set and very lightly golden on the bottom, but not browned, 15-20 minutes. Allow to cool to room temperature on the baking sheet.
• Transfer the cooled cookies to a wire rack. Group into like-sized pairs.
• Cover one cookie with a thin layer of jam and top with another cookie, lightly pressing down to seal to make a sandwich cookie. Repeat with the other pairs.

To make the glaze:

• In a double boiler (or heatproof bowl placed over a pot of simmering water), whisk together the powdered sugar and water. Cook, stirring often, until thickened enough to coat the cookies.
• Stir in the vanilla extract (if using) and 1/2-1 drop of the pink or red coloring to create a vibrant pink glaze.
• Remove the bowl from heat to immediately coat the sandwich cookies.
• Pour a spoonful of the glaze over the top of the cookie, starting from the center and then along the edges to completely coat the top and sides in a thin layer.
• Stir the glaze in the bowl between coating the cookies as needed to keep it from setting.
• Allow the Napolitaines to rest at room temperature at least 2 hours and ideally overnight to allow the flavors to settle and glaze to set.
• Once set, use an offset spatula to remove the Napolitaines from the wire rack. Store in an airtight container at room temperature for up to a week.