Place the freeze dried blueberries in a coffee grinder and pulse until finely ground. Sift the almond flour, powdered sugar and blueberry powder through a fine-mesh sieve into a large bowl and set aside.
In the bowl of a stand mixer fitted with the whisk attachment add the egg whites and cream of tartar. Beat on low speed. When the egg whites start begin to increase in volume, gradually add the granulated sugar until fully incorporated.
Fold in the almond flour mixture one third at a time with a spatula. Continue folding and turning, scraping down the bowl until it flows like thick lava, about 2 minutes. Transfer the batter to a pastry bag fitted with a 1/4-inch round tip.
Line the baking sheet with silicon mat or parchment paper. Pipe the macarons on the prepared baking sheet in 1-inch circles, spacing at least 1-inch apart. Firmly tap the baking sheet a few times against the counter to release any air bubbles. Let the macarons sit on the counter for 40-60 minutes until dry to the touch.
To make the lemon buttercream,
in the bowl of a stand mixer fitted with the paddle attachment beat the softened butter, powdered sugar, milk and lemon zest, scraping bowl occasionally, until smooth and creamy about 3-5 minutes.