The color of your strawberry curd will reflect the color of your strawberries. For the deepest curd, use ripe off the vine strawberries when you can find them.
You can also cook down your strawberries with the lemon juice and white sugar without puréeing them. Use an immersion blender or transfer the cooked mixture to a blender to break down any pieces that are still there after cooking.
Taste the strawberry mixture after the initial cook time (before straining and adding the eggs) for sweetness. If your strawberries are not as ripe, you may want to add more sugar.
Since we’re heating the eggs and cooked strawberry mixture from room temperature, the eggs will not curdle or scramble. Do not add the eggs to the strawberry mixture while it’s still hot. Passing the strawberry mixture through a sieve will help cool down the mixture quite a bit.
Between the heat and whisking, the curd gets foamy while cooking. As the curd begins to thicken, the foam settles down, and then the addition of the butter eliminates the foam after cooking.