In a medium bowl, whisk together flour, baking powder, and salt.

In a large bowl using an electric mixer, cream butter and sugar for 2–3 minutes until light and fluffy.

Add egg, vanilla, and water; beat until the dough is silky and smooth.

Gradually mix in the flour mixture on low speed until the dough just comes together.

Divide the dough in half. Place each half between parchment sheets and roll into 9×6-inch rectangles, about 1/8-inch thick.

Tint one rectangle evenly with red gel food coloring.

Chill both dough rectangles for 30 minutes.

Stack the red rectangle on the plain one, trim edges to align, then roll into a tight 9-inch log.

Wrap the log in plastic and chill for 2 hours.

Preheat oven to 350°F and line baking sheets with parchment paper.

Slice the chilled log into 1/4-inch rounds and place 2 inches apart on the prepared sheet.

Bake for 10–12 minutes until the edges are set and just starting to color.

Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.