1/2 cup fresh lemon juice
1/4 cup fresh lime juice
1 tbsp finely grated lemon zest
1 tbsp finely grated lime zest
3/4 cup sugar
3 large eggs
1 stick (1/2 cup) unsalted butter, room temperature

1. In a medium saucepan, whisk together the lemon juice, lime juice, lemon zest, lime zest, sugar and eggs. Cut the butter into bits and add it to the saucepan.

2. Turn on the heat to medium-low and cook the mixture gently, whisking constantly, until it thickens up enough to hold the marks of the whisk and is just about to come to a simmer. This takes me usually around 20-25 minutes — better to be gentle than to curdle your eggs. The end mixture will be a buttery, creamy light yellow.

3. Remove from the heat and place into a bowl to cool. Strain it if you want to get rid of the zest. Place a piece of plastic wrap on the surface of the curd to prevent a skin from forming as it cools. Store the curd in the fridge.