Preheat the oven to 350°F / 175°C. Line a cookie sheet with parchment paper or a silicone baking mat.
In a small saucepan set over medium heat, brown the butter. Stir the butter occasionally until it turns amber in color and develops little brown specks.
Transfer the brown butter to a small heat-safe bowl. You should be left with at least 90g of brown butter (but not more than 95g). If you have a little less than 90g, just add in some water until you reach it.
Place the brown butter in the freezer for 5 minutes to cool down.
In the meantime, prep your white chocolate and lavender sugar.
Chop up the white chocolate and set aside. Then, blend the 75g of granulated sugar with the dried culinary lavender in a food processer to break up the lavender into smaller pieces. Pour the lavender sugar into a bowl and set aside.
Once the brown butter has cooled, mix in both sugars.
Whisk in the egg and lavender extract until well combined.
Add in the flour, baking soda, baking powder and salt. Use a rubber spatula to fold the mixture together just until a few flour streaks remain.
Add in the white chocolate and fold just until no flour streaks remain.
Scoop out heaping 3 tbsp. scoops of dough, and roll each cookie ball in the lavender sugar. Place the cookies at least 2" apart on the baking sheet to allow room for spreading.
Top each cookie with additional white chocolate if desired, and bake for 12-14 minutes, or until the edges of the cookies are golden brown.
Immediately after taking the cookies out of the oven, you can take a bowl that is slightly larger than the cookies and swirl it around over the cookies to make them a little more uniform and circular.
Serve and enjoy!