Rinse the strawberries, cut the top, then process them in a food processor until smooth.
Measure one cup of strawberry puree, and then add the lemon juice.
Mix the egg and egg yolks into the sugar, in a separate bowl.
Pour the fruit juice and egg mixture into a medium saucepan and mix to incorporate.
Cook over medium or medium-low heat while constantly stirring with a wooden spoon until the mixture has thickened and it coats the back of a spoon.
Remove from the heat, and run it through a fine sieve over a clean bowl.
Add the butter to the warm curd and gently stir until the butter has melted.
Allow the curd to cool for about one hour at room temperature. Refrigerate for up to 5 days.