In a large bowl, cream together softened butter, granulated sugar, and brown sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

In a separate bowl, whisk together flour, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Stir in the green food coloring until the dough is evenly colored.

Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.

Scoop rounded tablespoons of dough onto the prepared baking sheets, about 2 inches apart.

Bake for 9-11 minutes, or until the edges are lightly golden and the centers are still soft.

Let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.

While the cookies are cooling, melt the white chocolate chips with vegetable oil in a microwave-safe bowl in 30-second intervals, stirring in between, until smooth.

Dip the tops of the cooled cookies into the melted white chocolate and immediately sprinkle with red sanding sugar.

Allow the chocolate to set completely before serving.