In a medium saucepan, rub together sugar and zest with fingertips. Whisk in cornstarch and salt. Add lemon juice and ½ cup (120 grams) water, whisking until smooth. Whisk in egg yolks and gelatin. Cook over medium-high heat until thickened, about 8 minutes. Remove from heat, and stir in butter.
Line a rimmed baking sheet with plastic wrap. Pour curd onto prepared pan, and press another piece of plastic wrap directly onto surface of curd. Place pan on a wire rack, and let cool to room temperature. Refrigerate until chilled.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/meyer-lemon-blueberry-pie/