Step 1: In a medium bowl, whisk together the flour, baking powder, salt, and cocoa powder. Set aside.
Step 2: In a large bowl, using an electric mixer, cream together the softened butter and granulated sugar until light and fluffy, about 2-3 minutes.
Step 3: Beat in the egg, vanilla extract, red gel food coloring, and white vinegar (if using) until well combined and the color is even and vibrant.
Step 4: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix. The dough will be soft.
Step 5: Divide the dough in half, flatten each half into a disk, wrap tightly in plastic wrap, and chill in the refrigerator for at least 1-2 hours, or up to 2 days. Chilling is crucial for easy handling and to prevent spreading.
Step 6: Preheat your oven to 375°F (190°C). Line baking sheets with parchment paper or silicone mats.
Step 7: On a lightly floured surface, roll out one disk of dough to about 1/4-inch thickness. Use your favorite cookie cutters to cut out shapes. Place the cut-out cookies about 1-2 inches apart on the prepared baking sheets.
Step 8: Bake for 8-10 minutes, or until the edges are just set and the cookies are lightly puffed. Do not overbake, as they will continue to firm up as they cool. The centers should still look slightly soft.
Step 9: Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Step 10: While cookies cool, prepare the cream cheese frosting (if using). In a medium bowl, beat softened cream cheese and butter together until smooth. Gradually beat in powdered sugar and vanilla extract until creamy. Add milk, a tablespoon at a time, until desired consistency is reached.
Step 11: Once cookies are completely cool, spread or pipe the cream cheese frosting onto each cookie. Store frosted cookies in an airtight container in the refrigerator for up to 3-4 days.