No need to preheat the oven yet, this dough needs to chill.
Place the flours, bicarb and chocolate chunks into a medium sized bowl and stir briefly, until combined.
Place the butter, sugars and zest into a large bowl, or the bowl of your stand mixer and beat until light and fluffy, about 2 minutes on med-high speed.
Add in the eggs and lemon extract and mix until smooth and well incorporated.
Add in the vanilla extract and mix until combined.
Add in the flour mix and mix on low until a dough forms.
Tip the dough into a large bowl and cover with cling film. Place in the fridge for at least 6 hours, overnight if possible.
Once the dough is chilled, preheat the oven to 180 degrees C/350F and line 2-3 baking trays.
Use a 1.5 or 2tbsp cookie scoop and place dough balls 2 inches apart, 12 to a standard baking tray.
Flatten the dough balls ever so slightly, to make sure they don't roll off when you take them to the oven!
For 1.5tbsp cookies place in the oven for 8-9 minutes. For 2tbsp cookies, place in the oven for 10-12 minutes.
Cookies are done when very lightly golden around the edges and soft and underdone in the middle.
Leave to cool on trays for at least 10 minutes, before transferring to a wire rack to cool completely.
Cookies will keep soft in an airtight container at room temperature for up to a week.