In a medium saucepan, bring 1 cup of water and ½ cup of unsalted butter to a rolling boil over medium heat. Once boiling, remove from heat and quickly stir in 1 cup of choux pastry flour until a smooth dough forms. Allow the dough to cool for about 5 minutes, then incorporate 4 room-temperature eggs one at a time, mixing vigorously until the dough is shiny and pulls away from the sides of the pan.

Transfer the choux pastry dough into a piping bag fitted with a large round tip. Line a baking sheet with parchment paper, then pipe long strips of dough about 4 inches long. Bake in a preheated oven at 375°F (190°C) for 25-30 minutes, until the eclairs are puffed up and golden brown. Do not open the oven during baking.

In a large mixing bowl, whip 1 cup of chilled heavy cream until soft peaks form. Gently fold in the zest and juice of 1 large lemon along with ¼ cup of granulated sugar. Mix until fully combined and creamy.

For the raspberry glaze, blend 1 cup of fresh or thawed raspberries with 1 cup of powdered sugar until smooth. Adjust sweetness by adding more powdered sugar or blend in a touch of lemon juice.

Once the eclairs have cooled completely, slice each one in half lengthwise. Fill each eclair with the lemon cream filling, then drizzle or dip the tops into the raspberry glaze.