Step 1

Place a medium saucepan over low heat. Add the raspberries, sugar, and water to the pan and stir to combine. Increase the heat to medium and bring to a simmer, stirring occasionally to prevent sticking. Reduce the heat to hold the mixture at a gentle simmer and cook until the berries release their liquid and soften and the sugar dissolves, about 5 to 7 minutes. If you are using frozen berries, this process may take a few extra minutes to allow for the frozen fruit to thaw.

Step 2

Remove the pan from the heat and allow the mixture to cool slightly. When the mixture is cool enough to handle safely, strain the mixture through a fine sieve or a colander lined with cheesecloth to remove the seeds and fibrous pulp. Discard the solids. You should be left with a colorful raspberry syrup.

Step 3

In a small bowl, combine the lemon juice, cornstarch, and egg yolks. Whisk or stir until smooth. Add this smooth paste to a clean pan with the raspberry syrup. Place the pan over low heat and heat while stirring constantly until the mixture comes to a simmer and warms enough to allow the starch to thicken the syrup. Remove the pan from the heat.

Step 4

A perfectly thickened curd will be what the French call “Nappe”. Nappe is a fancy term for the consistency a sauce reaches when it is thick enough to coat a dish without being too thick. Checking to see if a curd or custard is nappe is simple. Immerse a clean spoon into the mixture; remove the spoon, turning it so that the back of the spoon is facing you. Run a finger down the length of the spoon from the handle to the tip. If a clean path is created and the curd remains on both sides of the spoon, you have achieved nappe. If not, simply continue to cook the sauce while whisking until it thickens properly.

Step 5

Add the butter and salt to the curd and whisk to combine. I like to strain my curd a second time to ensure that there are no lumps or bits of scrambled egg in the finished curd, but this step can be skipped if you prefer.

Step 6

Transfer the finished curd to a large bowl or Mason jar with a tight fitting lid. Chill until ready to use. Curd can be kept in the refrigerator for one week.