Preheat the oven to 250 F and line 2 baking sheets with parchment paper or a nonstick mat.
In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites on medium-high speed until they start to become frothy.
Add the caster sugar a little bit at a time until the meringue is close to forming stiff peaks.
Add the vanilla extract and beat until the meringue forms stiff peaks.
If desired, transfer half of the mixture to a separate bowl and fold in 1/2 tsp pink or red gel food coloring.
Spoon into a piping bag fitted with your favorite tip (or no tip!) and pipe 1" meringues onto baking sheets. Immediately top with sprinkles.
Bake until the meringues are firm and dry, about 1 hour. Turn off the oven but do not open the door. Leave the meringues in the oven until they have cooled completely (1-2 hours).
Notes
Store meringue cookies in an airtight container at room temperature for up to 1 week. You can substitute caster sugar with granulated sugar in a 1:1 ratio. You will get a slightly denser meringue, but still super yummy!