Prepare two baking sheets with parchment paper or silicone mats. Sift together almond flour and powdered sugar twice to remove any lumps. Set aside.

In a clean metal or glass bowl, beat the aged egg whites with cream of tartar on medium speed until foamy. Gradually add granulated sugar one tablespoon at a time, then increase speed to high and beat until stiff, glossy peaks form, about 4-5 minutes.

Fold the ground lavender into the meringue gently. Add the almond flour mixture all at once and fold using a flexible spatula, pressing against the bowl sides. Continue folding until the batter flows like lava and a ribbon drizzled on the surface disappears within 30 seconds.

Transfer batter to a piping bag fitted with a round tip. Pipe 1.5-inch circles onto prepared sheets, spacing them 1 inch apart. Tap sheets firmly on the counter 5-6 times to release air bubbles.

Let piped shells rest at room temperature for 20-40 minutes until a dry skin forms on the surface. Touch gently — if no batter sticks to your finger, they're ready. Preheat oven to 300°F during this time.

Bake one sheet at a time for 14-16 minutes, rotating halfway through. Shells are done when they don't wiggle when touched gently. Let cool completely on the baking sheet before removing.

For the ganache, heat cream until just simmering. Pour over chopped white chocolate and let stand 2 minutes. Stir until smooth, then mix in lavender honey and butter until glossy. Refrigerate 30-45 minutes until thick enough to pipe.

Match shells into pairs by size. Pipe or spread ganache onto flat side of one shell, then sandwich with its partner. Press gently until filling reaches the edges.

Refrigerate filled macarons in an airtight container for 24 hours before serving to allow flavors to meld and texture to soften perfectly.