Add butter to a large saucepan and place over medium heat, whisk constantly. After a couple of minutes, the butter will begin to brown and turn a nice golden colour on the bottom of the saucepan. Continue to whisk and remove from heat as soon as the butter begins to brown and gives off a slightly nutty aroma. Immediately transfer the butter to a medium bowl to prevent burning. Set aside until cool enough to touch.
Using an electric mixer, mix the brown butter and both sugars until well combined, about 1 minute. Beat in the egg, egg yolk, vanilla, and yogurt until combined.
In a separate large bowl, mix together the flour, baking soda, and salt. Slowly add the dry ingredients to the wet ingredients and beat on low-speed just until combined. Add both chopped chocolate and mix with spoon until just incorporated.
Chill the dough for 2 hours in the refrigerator.
Once dough is chilled, preheat the oven to 350 degrees F and line a baking sheet with parchment paper. You might need to take out the dough and thaw it out a bit before measuring the dough Once your ready to bake, measure 2 heaping tablespoons of the dough or use a medium cookie scoop. It doesn't have to be perfectly rolled. Place dough balls on cookie sheet, 2 inches apart.
Bake the cookies 9 minutes or until the edges of the cookies begin to turn golden brown. They will look a bit underdone in the middle, but will continue to cook once out of the oven.
Cool the cookies on the sheets for 5 minutes to allow them to set up, then sprinkle each cookie with sea salt. Cool the cookies on the sheets for 5 minutes to allow them to set up, then sprinkle each cookie with sea salt.