To make macaron shells, place the freeze-dried raspberries for both shells and filling in a ziplock bag and roll with a rolling pin until fine powder. (Alternatively, you can place freeze-dried raspberries between two sheets of parchment paper and crush them with a rolling pin.)
Sift the crushed raspberries through fine mesh sieve to remove the seeds.
In a medium bowl, sift together almond flour, powdered sugar and 3 tablespoons of powdered raspberries. (Reserve 1 tablespoon of raspberry powder for the filling.) Sift everything one more time and set aside.
In a large mixing bowl with whisk attachment, beat the egg whites on medium speed until foamy.
Add cream of tartar and continue to beat. (Cream of tartar is optional, and is added to stabilize the egg whites.)
Slowly add sugar one tablespoon at a time. Continue to beat until hard peaks form. (Watch this meringue video for more information.)
Add food coloring and beat on medium speed for one more minute.
Sift the almond flour mixture over the whipped egg whites. Gently fold the mixture running the spatula clockwise from the bottom, up around the sides and cut the batter in half. The batter will look very thick at first, but it will get thinner as you fold. Be careful not to over mix it though. Every so often test the batter to see if it reached the right consistency. To test the batter, drop a small amount of the batter and count to ten. If the edges of the ribbon are dissolved within about ten seconds, then the batter is ready. Again do NOT mix again at this point. But if you still see edges, fold the batter couple more times and test again. This step is so crucial, so please make sure to test often to ensure not to over mix the batter.
Transfer the batter into a pastry bag with a round tip. (I used this Wilton 1A plain round tip
Pipe out 1-inch rounds about an inch apart on two baking sheets lined with parchment paper. You'll get about 46-50 shells.
Tap the baking sheets firmly on the counter a few times to get rid of any air bubbles. If you don’t release the air bubbles, they will expand during baking and crack the beautiful macarons shells.
Let the macarons rest and dry for 15-30 minutes. On a humid day, it might take an hour or so. To see if it’s ready to be baked, lightly touch it. If the batter doesn’t stick to your finger, then it’s ready.
Preheat the oven to 300°F (150°C).
Bake the macarons for 18-20 minutes. To check the doneness, remove one macaron. If the bottom does not stick, they are done.
Transfer to wire rack to cool for 15 minutes, and then carefully remove from the baking sheets.
To make the filling, in a mixing bowl with whisk attachment, beat the butter and powdered sugar until fluffy, about 2 minutes.
Melt the white chocolate chips in microwave according to package directions. (I microwaved mine for 1.5 minutes at 50% power. Stirred and microwaved for another 30 seconds at 50% power. Stirred again and microwaved for 15 seconds at 50% power.)
Add the melted white chocolate, raspberry powder, lemon juice and pinch of salt to the whipped butter mixture. Beat until the filling is smooth and well combined.
Transfer the buttercream into a pastry bag and fill the macarons.
To make white chocolate coating, melt white chocolate in microwave as described above. Dip macarons half way and place on a wire rack. If desired, sprinkle more raspberry powder.
Macarons are best when served the next day. Store the filled macarons in airtight container in the fridge for up to 5 days. You can also freeze the filled macarons in airtight container for up to 5 months.