see recipe link above for 'Home-Made Lemon Curd' recipe
Prepare the macaron batter first. Place the almond flour and confectioner's sugar into a fine mesh sifter and sift the flour and sugar into a large bowl. Sift through twice if desired for a more smooth finish on the macarons.
Place the eggs white and granulated sugar into a mixer bowl and whisk on high speed for 2 to 3 minutes, just until stiff peaks form; don't overmix. Add the food coloring and lavender oil and mix again for about 20 seconds, just until incorporated. Transfer the egg whites into the dry ingredients. Use the 'fold and flatten' method, folding the meringue into the flour and flattening it against the mixing bowl. Fold until the batter reaches ribbon stage - it should ribbon of the spatula and settle down within 10 to 15 seconds.
Line two large baking sheets with parchment paper or a silicone mat. Transfer the macaron batter into a pastry bag tipped with a simple round tip. Pipe 1-inch dollops of the batter onto the prepared paper, spacing about 1 1/2-inches apart. After piping the entire pan, tap the baking sheet again your work surface to release any trapped air bubbles. Allow the cookies to rest at room temperature for at least an hour, for a thin shell to form on the outside.
Preheat the oven to 320F and bake the rested cookies for 18 to 19 minutes. Please note - each oven bakes slightly differently and because this recipe requires precise temperature, your oven temperature and baking time might vary by a few degrees and minutes. Allow the cookies to cool on the pan.
Meanwhile, prepare the blackberry buttercream. Place the softened butter, confectioner's sugar, citric acid and food coloring into a large mixing bowl. Whisk on high speed with a mixer or hand whisk for 3 to 4 minutes, until the frosting is fluffy. Add the blackberry preserves last and mix for 5 to 10 seconds, just until incorporated. Place the frosting into the refrigerator to set for at least 30 minutes; do this while the cookies are baking and cooling.
Assembling the Cookies:
To assemble the cookies, first pair them off by size. Transfer the buttercream into a pastry bag tipped with a star tip; I used French star tip #4. Pipe a ring of frosting onto the cookies, leaving the center empty. Pipe a dollop of lemon curd into the center, then sandwich the cookies together. Place the assembled cookies into the fridge to set for 30 minutes, then transfer into an airtight container and refrigerator for at least 1 day, allowing the cookies to mature. Remove the macarons from the fridge about 30 minutes before enjoying, to allow the frosting to soften.