Cut parchment paper to fit bottom of 13" x 10" baking tray. Draw twenty 3.3 cm circles on paper with pencil, evenly spread out.

Place piping tip #802 in piping bag. Cut tip of bag to fit piping tip. Tie bag just above piping tip with rubber band.

Place almond flour and icing sugar in food processor. Blitz till mixture looks lump free, scraping down as necessary, then blitz a bit more (to be doubly sure all lumps are obliterated). Alternatively, sift almond flour and icing sugar.

Whisk egg white on slow speed till thick foam forms. Gradually add castor sugar, still whisking. Reduce speed. Continue to whisk till firm peak stage, i.e. peak is hooked. Reduce to manual speed. Continue to whisk till just hitting stiff peak stage, i.e. peak is straight. (Meringue is now smooth, not grainy.)

Sprinkle half of almond mixture on meringue. Cut with spatula till almond mixture is wet. Sprinkle with remaining almond mixture. Cut as before. Fold till just evenly mixed.

Fold batter till colour is even and texture is smooth, pausing now and then to scrape down spatula.

Continue folding, pausing every 10-15 folds to drop batter from about 25 cm high. When batter moves ever so slightly after landing, it's almost ready.

Keep folding, now pausing to observe every 3-5 folds. When batter oozes slightly after you stop folding, it's ready.

Transfer batter into piping bag. Remove rubber band. Twist top of piping bag tightly, squeezing batter downward.

Pipe small dollops of batter in corners of baking tray. Place parchment paper on tray, pencilled side facing down. Press paper against batter so that it sticks well. Pipe using drawn circles as guide, avoiding batter that's under parchment paper.

Rap baking tray against worktop – hard, 4-6 times – till tips of batter disappear or almost disappear. Prick visible air bubbles with skewer. Smooth holes and remaining tips.

Set tray aside till batter isn't sticky when touched lightly, about 30 minutes depending on the weather. (I put the tray in front of a table fan turned on low because Singapore is very humid.)

Whilst macaron batter is drying, preheat oven to 135°C. When batter is ready, bake on middle shelf of oven for 30 minutes.

Remove tray from oven. Drag parchment paper onto wire rack. Leave till macarons are cool. Carefully peel parchment paper from macarons.

Separate macaron shells into pairs that are same size. Pipe buttercream on one shell and top with the other.

Place macarons in fridge, covered, for a few hours or up to a few days. Remove from fridge before serving and allow to come to desired level of softness.