Sift almond flour and powdered sugar together twice into a large bowl. Discard any large bits of almond. For best results, pulse briefly in a food processor then sift.

In the clean, dry bowl of a stand mixer, whisk egg whites on medium speed until foamy. Add cream of tartar (if using). Gradually add granulated sugar, a tablespoon at a time, increasing speed to medium-high. Continue whipping until stiff, glossy peaks form (when you lift the whisk, the meringue should hold its shape firmly).

If desired, add 2-3 drops of gel food coloring to the meringue and mix briefly until just combined.

Add the sifted dry ingredients to the meringue. Fold gently with a rubber spatula, using a 'cut and fold' motion, scraping down the sides of the bowl. Continue folding until the batter reaches the 'lava' consistency – it should flow slowly off the spatula in a thick ribbon and you should be able to draw a figure 8 with it before it breaks. Be careful not to overmix; stop folding once it reaches this consistency.

Transfer the macaron batter to a piping bag fitted with a round piping tip (like Wilton 1A). Pipe 1.25-inch circles onto silicone baking mats or parchment-lined baking sheets, leaving about 1 inch between shells.

Firmly tap the baking sheets on the counter 2-3 times to release any trapped air bubbles. Use a toothpick to pop any remaining visible bubbles. Let the piped shells rest at room temperature for 30-60 minutes, or until a skin forms and they are dry to the touch (you should be able to gently touch them without batter sticking to your finger).

Preheat oven to 300°F (150°C). Bake one tray at a time for 12-14 minutes, rotating the tray halfway through baking for even cooking. Shells are done when they have developed 'feet' and don't wobble when gently touched. Let cool completely on the baking sheet before attempting to remove them.

While shells are baking/resting, prepare the jam. In a small saucepan, combine finely diced peaches, granulated sugar, and lemon juice. Cook over medium-low heat, stirring occasionally, until peaches soften and release their juices (about 5-7 minutes).

In a small bowl, whisk cornstarch and cold water together to create a smooth slurry. Add the slurry to the simmering peaches, stirring constantly. Cook for another 1-2 minutes until the jam thickens to your desired consistency. Remove from heat and let cool completely.

In the bowl of a stand mixer fitted with the paddle attachment, beat softened unsalted butter on medium speed until creamy (about 2-3 minutes). Add softened cream cheese and beat until smooth and thoroughly combined, scraping down the sides of the bowl as needed.

Gradually add sifted powdered sugar and vanilla extract. Beat on low speed until combined, then increase to medium-high and beat for another 2-3 minutes until the buttercream is light, fluffy, and smooth. Add a pinch of salt to balance the sweetness.

Once macaron shells and fillings are completely cool, transfer the cream cheese buttercream to a piping bag fitted with a round tip. Transfer the peach jam to a separate small piping bag (or use a small spoon if preferred).

Match up similar-sized macaron shells. Take one shell and pipe a ring of cream cheese buttercream around its outer edge. Spoon a small amount of the cooled peach jam into the center of the buttercream ring. Gently top with another macaron shell, twisting slightly to secure it.

Place assembled macarons in an airtight container and refrigerate for at least 24 hours to allow them to 'mature.' This process softens the shells and melds the flavors, resulting in the best texture and taste.