Preheat the oven to 300°F.

Separate the egg whites from the yolks, if using fresh eggs. Measure out 100 grams of whites (about 3 large eggs).

In a large bowl, sift the icing sugar and almond flour together.

Sift a second time to make sure there are no clumps. Discard any that remain.

In a stand mixer fitted with the whisk attachment, beat the egg whites and cream of tartar on high until foamy.

Turn the mixer down to its lowest setting and slowly add the granulated sugar. Make sure all of it is incorporated.

Turn the mixer back up to high and beat until peaks form. Don't overbeat.

Pour the almond flour and icing sugar mixture into the egg whites.

Fold with a rubber spatula until the batter flows like a ribbon.

Line a baking sheet with a silicone mat and macaron template.

Fit a pastry bag with a Wilton #12 round tip or a Wilton 1A round tip, and trim the bag as needed.

Pour the batter into the bag.

Pipe circles onto the prepared sheet, stopping when the batter reaches the lines on the template. You should get about 48 shells.

Rap the sheet on the counter to release air bubbles. Pop any small bubbles with a scribe or toothpick.

Rest for 30 minutes, until the shells have formed a skin and are no longer tacky.

Bake at 300°F for 13-15 minutes.

Wiggle a shell to check. If it doesn't move from its feet, it's done. If it does, bake another minute and check again.

Cool the shells completely on the tray.

In a bowl, beat the softened butter, brown sugar, and powdered sugar until light and fluffy.

Add the oat flour, vanilla, and salt. Beat until combined.

Beat in the cream, 1 tablespoon at a time, until the buttercream is smooth and holds its shape for piping.

Fold in the ½ cup mini chocolate chips.

Remove the cooled shells from the tray and pair them up by size.

Pipe a ring of cookie dough buttercream onto half of the shells. Top with mini chocolate chips.

Sandwich each with its pair. Repeat to assemble all the macarons.

Refrigerate for at least 24 hours so they can mature. Macarons taste best after a day's rest.

Take them out of the fridge 20 minutes before serving.

Refrigerator: Store in an airtight container for 3-5 days.

Freezer: Freeze for up to 3 months.