Prepare the Lemon Curd: In a heatproof bowl, combine 2 large eggs, 2 egg yolks, ¾ cup granulated sugar, 1 tablespoon lemon zest, and ½ cup freshly squeezed lemon juice. Place the bowl over a saucepan filled with simmering water (bain-marie). Whisk constantly for about 10–20 minutes until thickened, reaching a temperature of 170°F (75°C).

Check Consistency: Continue whisking as the curd cooks. After about 15 minutes, check that it leaves a clear path when you run your finger through it and registers 170°F (75°C).

Strain Mixture: Once thickened, remove from heat and strain through a fine mesh sieve into a clean bowl to remove lumps.

Incorporate Butter: Gradually whisk in ½ cup of room-temperature unsalted butter pieces until melted and smooth.

Assemble the Tart: Pour the cooled lemon curd into the prepared tart crust and smooth the filling. Refrigerate for at least 4 hours or overnight.

Serve and Enjoy: Once chilled, slice and garnish with powdered sugar or fresh berries as desired.