Preheat the oven to 200°F (95°C). Line 2 baking sheets with parchment paper.
2. Step
Add the sugar to a baking sheet and bake for 7 minutes. The edges may begin to caramelize – this is good! Remove the sugar from the oven and leave the oven on.
3. Step
In a large clean, dry bowl, whip the egg whites with an electric hand mixer on low speed until foamy, then add the salt. Continue whipping on high speed until medium peaks form.
4. Step
Add the toasted sugar to the egg whites 1 tablespoon at a time, increasing the mixer speed gradually as you add more sugar. Once all of the sugar is incorporated, continue whipping for 5-7 minutes, until the meringue is very thick and shiny. Add the vanilla, whipping until just incorporated.
5. Step
Prop open a piping bag or zip-top bag in a tall drinking glass. Using wooden skewers, lightly paint 2 thin stripes of different-colored gel food coloring on opposite sides of the bag. Paint additional bags with more colors, if desired.
6. Step
Fill each bag with the meringue batter, dividing evenly amongst different colors, if using.
7. Step
Pipe 1-inch (2-cm) wide “kisses” of meringue onto a baking sheet about ½ inch (1 cm) apart.
8. Step
Bake for about 1 hour, or until you can easily lift a kiss off of the paper.
9. Step
Cool the meringues on the baking sheet at room temperature until no longer warm.
10. Step
To fill, pipe icing around the edge of a cookie and spoon a small dollop of jam into the center. Sandwich with another cookie.
