Swiss meringue buttercream, vanilla

Bring all ingredients to room temperature. Cut the butter into tablespoon pieces; it should be pliable and waxy, not stiff and not melted.

Combine egg whites, cream of tartar, sugar and salt in a heat-proof stand mixer bowl.

Set the bowl over a saucepan of hot water and whisk until the sugar has fully dissolved and the mixture is syrupy and thick.

Continue warming to 160F to pasteurise the whites. Test for dissolved sugar by rubbing a dab between two fingers; no grit means dissolved.

Whip with the whisk attachment to very stiff, glossy peaks, letting the mixture cool to room temperature as it whips.

Add the butter one piece at a time on medium to medium-high, waiting for each piece to disappear before the next.

If the mixture curdles and looks like ricotta, switch to the paddle and beat without more butter until the temperature comes up and it smooths out; warming the outside of the bowl by hand helps.

Add the remaining butter, scrape the bowl and give a final mix with the paddle. Do not over-beat.

Beat in the vanilla bean seeds and a splash of vanilla extract. Keep added liquid to a minimum or the emulsion breaks.

To store, press plastic directly onto the surface and freeze or chill. Bring fully to room temperature before serving.