In a medium saucepan, combine 1/4 cup of water and 4 tablespoons of lemon juice over medium heat. Once it begins to simmer, add 6 peeled, cored, and chopped apples. Cover the saucepan and cook for about 20 minutes, stirring occasionally, until the apples are very soft.

Remove the saucepan from heat and let the apples cool for a few minutes. Mash the soft apples until they form a chunky purée. For an ultra-smooth texture, press through a fine sieve into a bowl.

In a medium bowl, crack 2 whole eggs and add 2 egg yolks. Whisk them vigorously until smooth. This egg mixture will thicken your Apple Curd.

If using cornstarch, combine 1 tablespoon of cornstarch with 2 tablespoons of water. Stir until smooth, and set aside.

Return to the apple purée, add cubed 1/2 cup of unsalted butter and 1 1/2 cups of sugar. Pour in the whisked eggs and stir everything together.

Pour the mixture back into the saucepan and cook over low heat, stirring for about 15 to 20 minutes, until thickened.

Strain the thickened Apple Curd through a fine sieve into a clean bowl, allowing it to cool to room temperature.

Transfer to a sterilized jar or airtight container and refrigerate for at least 2 hours before using.