In a medium saucepan, combine 1 cup of filtered water and ½ cup unsalted butter over medium heat. Stir until the butter is melted, and the mixture comes to a simmer. Add 1 cup of all-purpose flour all at once, stirring vigorously with a wooden spoon for about 2-3 minutes until the dough forms a ball and pulls away from the sides of the pan.

Remove the saucepan from the heat and let the mixture cool slightly for about 5 minutes. Begin adding 4 room-temperature eggs, one at a time, mixing well after each addition until the dough is smooth and glossy.

Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper. Transfer the choux pastry into a piping bag fitted with a large round tip. Pipe long, even logs about 4 inches long.

Place the baking sheet in the preheated oven and bake for 25-30 minutes, or until the eclairs are golden brown. Remove from the oven and cool on a wire rack.

For the lemon cream filling, whisk together 3 eggs and ½ cup granulated sugar in a heatproof bowl. Place the bowl over simmering water, add the zest and juice of 2 lemons, stirring constantly until thickened.

For the raspberry glaze, blend 1 cup of raspberries until smooth and strain through a fine-mesh sieve. Mix the purée with 1 cup of powdered sugar until smooth.

Once the eclair shells are cooled, pierce one end of each pastry, fill with the lemon cream, and drizzle with raspberry glaze.