1. Preheat the oven to 300°F (150°C).
2. Line two baking sheets with parchment paper.
3. Prepare a pastry bag fitted with a plain round tip (about 1/2-inch or 2 cm wide).

For the Soup

1. In a food processor, grind together the powdered sugar and almond flour until super fine.
2. Sift the mixture through a fine-mesh sieve into a bowl to remove any large bits.
3. In the bowl of a stand mixer (or using a hand mixer), beat the egg whites until soft peaks form.
4. Gradually add granulated sugar and continue beating for 2 minutes, until stiff, glossy peaks form.
5. Mix in the vanilla extract or vanilla bean powder.
6. Gently fold the sifted almond flour mixture into the beaten egg whites using a rubber spatula.
7. Fold until the batter is smooth, shiny, and flows off the spatula in thick ribbons (about 40-50 folds).
8. Transfer the batter into the piping bag.
9. Pipe 1-inch (3 cm) circles, spaced 1 inch apart onto the lined baking sheets.
10. Tap the baking sheet firmly on the counter a few times to release air bubbles.
11. Let the piped macarons rest at room temperature for 30 minutes until a thin skin forms on top.
12. Bake in the preheated 300°F (150°C) oven for 15-18 minutes until the macarons develop feet and are set.
13. Let them cool completely before removing from the baking sheets.

For the Vanilla Buttercream Filling

1. In a bowl, beat the softened butter until smooth and fluffy (about 2 minutes).
2. Gradually add the powdered sugar, continuing to beat.
3. Mix in the vanilla extract and 1 tablespoon of heavy cream/milk.
4. Beat until the frosting is smooth and creamy.
5. If needed, add an extra tablespoon of heavy cream/milk to adjust consistency.
6. Match similarly sized macaron shells into pairs.
7. Pipe or spread a small amount of vanilla buttercream onto one macaron half.
8. Gently press another macaron shell on top to form a sandwich.
9. Refrigerate for 24 hours to allow flavors to meld (optional, but recommended).