Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a large mixing bowl, combine granulated sugar and fresh lemon zest. Use your fingertips to massage the zest into the sugar for 1-2 minutes until fragrant and the sugar takes on a light yellow tint.

Add softened butter and brown sugar to the lemon sugar mixture. Beat on medium-high speed for 3-4 minutes until light and fluffy.

Mix in egg yolk, vanilla extract, and lemon juice until well combined, about 1 minute.

In a separate bowl, whisk together flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed just until a few flour streaks remain.

Working quickly, remove frozen raspberries from the freezer and roughly chop them into small pieces.

Gently fold the frozen raspberry pieces into the cookie dough using a spatula with just 4-5 strokes (minimal mixing prevents color bleeding).

Using a 3-tablespoon cookie scoop, portion dough into balls and place on prepared baking sheets, spacing 5 cookies per sheet.

Sprinkle each cookie lightly with flaked sea salt if desired.

Bake for 12-15 minutes, until edges are lightly golden while centers remain soft.

Remove from oven and allow cookies to rest on the baking sheet for 5 minutes before transferring to a wire cooling rack.

Cool completely before storing in an airtight container.