In a small bowl, whisk together the powdered sugar and meringue powder.

Add the warm water and beat on low speed until combined. Turn to medium high speed and beat until the icing is glossy and holds stiff peaks. The icing should be thick but pipable. Mix in additional water or powdered sugar if needed.

Divide the icing into two bowls. Mix the desired amount of red gel food coloring into one of the bowls. Transfer the icing to a piping bag fitted with a leaf tip. Mix the desired amount of green food coloring into the other bowl. Cover with plastic wrap until ready to use.

Line a baking sheet with a piece of wax paper.

For larger poinsettias, pipe 4 poinsettia leaves in a cross shape. Let dry briefly. Pipe additional 4 poinsettia leaves in the spaces between the first leaves. Repeat to make additional poinsettias. To make smaller poinsettias, pipe 5 smaller leaves in a circle shape, making sure they touch in the center. Repeat to make additional poinsettias.

To add leaves, transfer the green icing to a piping bag fitted with a leaf tip. Pipe a small to medium leaf on the side of each poinsettia.

Place a white or yellow pearl sprinkle into the center of each of the poinsettias.

Let the icing decorations dry, uncovered, until hardened, about 2-3 hours.

In a medium bowl, whisk together the flour and salt. Set aside.

In a separate bowl, beat the butter and sugar until light and fluffy. Add the eggs and vanilla and beat until incorporated.

Add half of the flour mixture and mix on low speed until combined. Add the remaining half of the flour and mix until combined.

Roll the dough into a large ball and then flatten into a disk. Wrap in plastic wrap and refrigerate for 30-60 minutes.

Preheat the oven to 350 F. Line two baking sheets with parchment paper.

Transfer the dough to a floured surface and roll out to ¼ inch thickness.

Cut out the cookies using a large or medium size Mickey Mouse cookie cutter. Transfer the cut-out cookies to the prepared baking sheets and place in the refrigerator for 15 minutes.

Bake cookies for 9-12 minutes or until the edges are beginning to brown. Let cool for a couple minutes on the baking sheet before transferring to a wire rack to cool completely.

Place a piece of wax paper on your work surface. Set up two cooling racks near your work area.

Place 1 cup white chocolate melting wafers into a heat-safe bowl. Microwave until melted, stirring every 30 seconds.

Working one cookie at a time, use an off-set spatula to spread a layer of white chocolate onto the cookie.

Pour the white sprinkles onto the top of the cookie, making sure to cover all of the chocolate. Gently shake the excess sprinkles off of the cookie and onto the wax paper.

Set the cookie on the cooling rack. Repeat with remaining cookies, collecting and reusing the sprinkles from the wax paper as needed.

Let the cookies set for 15 minutes.

Gently remove the hardened poinsettia decorations from the wax paper. Dab the back of a poinsettia with melted white chocolate and gently press onto the cookies.

Let the cookies set 15 minutes before serving.