In a large mixing bowl, combine flour, cocoa, baking soda, baking powder, and salt. Mix well with a fork until fully combined.
In a separate large mixing bowl, combine butter and sugars with an electric hand or stand mixer. Mix until smooth.
Add in egg and vanilla and continue to mix until smooth.
Fold in dry mixture and continue to mix. It will be very crumbly at first.
Add in red coloring starting with about 3-4 large drops. Continue to blend until the dough becomes more formed and red. Add food coloring as you go. You may need to switch from electric mixing to hand mixing.
When your dough is complete, form into a tight ball and wrap in plastic wrap. Place inside the refrigerator for at least 2 hours or overnight.
After the chill time is complete, preheat your oven to 350°F/180°C and prepare a large baking sheet with parchment paper.
Roll out the dough on a floured surface. Roll evenly until the dough is about ¼ inch thick.
Use a heart shaped cookie cutter to cut the dough, then place the heart shapes on the baking sheet, about 2 inches apart from one another.
Bake cookies for 11-12 minutes, or until lightly browned on the edges.
When done, allow the cookies to cool on the baking sheet for 2 minutes before transferring to a cooling rack. Allow them to completely come to room temperature before proceeding.
When your cookies are at room temperature, prepare your frosting. Combine the powdered sugar and milk in a small mixing bowl and stir. It will be very thick at first. Continue to stir until the frosting has reached perfect smoothness and slowly falls off your fork or spoon. Add additional milk if needed, 1 tablespoon at a time.
Add frosting to a piping bag with a small round attachment. Pipe frosting onto the cookies in whatever design you desire. Allow frosting to harden for at least 30 minutes before serving.
Notes
Recipe Yield: You will get about 16 cut-out cookies using a 3-inch heart cookie cutter. You may use other cutters, but the yield will vary.
To get the brightest red velvet color, use gel food coloring.
Chilling the dough is important, as it will be difficult to work with if it's warm. Warm cut-out cookie dough will also spread too much on the baking pan.
Let the cookies cool completely before decorating.
Try Different Icing: The icing in this recipe is a very simple powdered sugar cookie icing. You can also decorate these with store-bought cookie icing, royal icing or buttercream if you like!
White icing looks great against the deep red of these cookies, but you can also tint the frosting other colors.
Decorating Ideas: Outline the hearts with simple lines, fill them in, or drizzle the icing to make easy decorations. You can also pipe names on these lovely hearts!
To Store: These cookies will stay fresh for up to 1 week when stored in an airtight container at room temperature. They can also be frozen for up to 3 months.
To Make Ahead: The dough for these cookies can be made and kept in the fridge for about 24 hours before baking. You can also freeze the dough for up to 2 months. Thaw in the fridge before using.