Add the egg whites to a large glass or metal bowl and bring to room temperature.

Add the almond meal, powdered sugar, and salt to a food processor and pulse until it is a fine powder. Set aside.

Add the cream of tartar to the egg whites and use a whisk attachment on a hand mixer (or stand mixer) and whisk until soft peaks form. While the mixer is running, slowly add the granulated sugar, about 1-2 tablespoons at a time. Continue mixing as you add all of the sugar and beat until stiff peaks form.

Add about 3 drops green food coloring (I probably used 1/2 teaspoon of Americolor gel paste in Leaf) and gently fold into the meringue 3 to 4 times.

Sift the dry ingredients into the egg whites. Use a spatula to gently fold the dry ingredients into the egg whites. Fold until completely incorporated and the batter runs off the spatula in long ribbons.

Line 2 baking sheets with silicon baking mats or parchment paper. Add the batter to a piping bag fitted with a Wilton 2A piping tip (round tip with a 1/2 inch diameter) and pipe the batter into 1 1/2 inch circles.

Once all the rounds are piped, gently lift and drop the baking sheets onto the counter several times to help pop any air bubbles. Carefully place a red heart sprinkle on half of the macarons.

Let the macaron shells sit uncovered at room temperature for 45-60 minutes to help form a dry shell on the outside.

When the shells have dried, preheat the oven to 300 degrees. Bake the shells for 10-12 minutes. Remove from the oven then leave the macarons on the baking pan for 5 minutes. Then carefully slide the silicon mats or parchment paper onto wire racks. Cool completely before carefully removing from the parchment paper or silicon mat. Make the buttercream while the macaron shells are cooling.

Add the butter to the bowl of a stand mixer fitted with the paddle attachment and beat until smooth.

Add half of the powdered sugar and a pinch of sea salt and beat on low until the sugar is mostly incorporated. Add the remaining powdered sugar and beat on low until combined. Increase speed to medium and beat for 3 minutes.

Stop the mixer and scrape down the bowl. Add the vanilla extract, whipping cream, and food coloring and beat for an additional minute on low, increasing the speed to medium once the whipping cream is incorporated.

Transfer the buttercream to a piping bag fitted with a Wilton 2A tip. Pipe a small amount of buttercream onto the 12 macaron shells that do not have heart sprinkles, make sure they are completely cooled first. Top each with the macaron shells with the heart sprinkles.