Using an electric mixer on medium speed, beat the softened butter and sugars together, about 2 minutes. Add the eggs and vanilla, increase the mixer speed to medium-high, and beat until mixture lightens and begins to thicken, about 1 minute. Scrape down the sides and bottom of the bowl as needed.
In a medium bowl, mix together the flour, cornstarch, baking soda, baking powder and salt.
With the mixer on low speed, slowly mix in the dry ingredients into the wet ingredients until just combined. Add the chopped chocolate and raspberries and mix on low for about 5-10 seconds until combined. Cover with plastic wrap and place in the fridge for 30 minutes.
Preheat oven to 350°F and line baking sheets with parchment paper.
Scoop out 2 tbsp-sized portions and gently roll into a ball with your hands. Place 3 inches apart on the baking sheet.
Bake for 10-12 minutes. You want the edges to be golden brown but the middle should still be soft. Allow the cookies to cool for 5 minutes on baking sheet before transferring to a cooling rack.
Notes
Use room temperature ingredients. You want your eggs to be the same temperature as everything else so it easily combines.
Measure the flour by weight so you get the exact amount needed.
Feel feel to use regular white chocolate chips instead of chopping your own.
Dice the raspberries and freeze them before adding to the dough to prevent too much bleeding. You can also use freeze-dried raspberries.
Use a cookie scoop for consistent cookie size, ensuring even baking.