Preheat oven to 225 degrees F. Line non-stick baking sheets with parchment paper or use the Silpat sheets to prevent the cookies from sticking.
Using your food processor, place the sugar, powdered sugar, and dried lavender flowers in the work bowl; process until ground to a fine dust.
In a large bowl using your electric mixer, beat egg whites until foamy. While beating, add salt, cream of tartar, and vanilla extract until soft peaks form. S till beating, very gradually, add sugar/lavender mixture (1 tablespoons at a time) to egg whites. Continue to beat until sugar has dissolved and stiff peaks form, approximately 2 to 3 minutes. Check out How To Make A Perfect Meringue.
Drop batter by tablespoonfuls onto prepared non-stick baking sheets, spacing about 1-inch apart. Also may use a piping bag fitted with a plain round tip
Bake, switching baking sheets halfway through, until meringues are dry and firm, about 2 hours. Remove from oven and cool completely on baking sheets.
NOTE: Do not bake on a humid day, or your meringues may not dry.
Meringues can be stored in an airtight container for up to five days.
Lavender Meringue Cookies Recipe: https://whatscookingamerica.net/Cookie/LavenderMeringueCookie.htm