In a food processor, pulse lilac blossoms (free of green stem) and sugar until the mixture is pale purple. Set aside.
In an immaculately clean bowl, beat egg whites until stiff peaks form. Start adding lilac sugar mixture one tablespoon at a time, whipping again until stiff peaks are formed after each addition.
Line a large baking sheet with parchment paper. Drop meringues by the spoonful into 12 roughly equal mounds. Using the back of a spoon, create a depression or "well". Bake in a preheated oven at 250 degrees (F) for approximately one hour or until the meringues are firm and lift away from parchment with ease. Cool completely.
To make Lemon Curd: Place egg yolks, lemon juice, lemon zest, sugar, and butter in a small saucepan. Over medium heat, and stirring constantly, cook until mixture thickens. A whisk moving through the mixture should leave a slight "trace". (This usually takes me a cautious 15-20 of vigilant attention).
Once the lemon mixture is adequately thickened, remove from heat and pass through a fine-mesh sieve into a bowl to remove zest and any "cooked" egg. Place a layer of parchment or plastic wrap directly on the warm curd and refrigerate until the curd is cold.
Spoon chilled curd into cooled meringues and serve. (Note: depending on the depth of depression in the meringues, you may a small amount of extra curd -- this is not a problem for most ;) )