Heat a medium saucepan on medium heat and add butter. Melt until bubbly and lightly browned. Remove from heat and let solidify at room temperature.
In a stand mixer, cream brown butter with 1/2 cup white sugar and 1/3 cup brown sugar until light and fluffy. Add 1 whole egg, 1 tsp vanilla extract, and sour cream, and mix until combined.
In a separate bowl, sift together the flour, baking soda, baking powder, and 1 tsp kosher salt. On low speed, add your flour mixture to your stand mixer and mix for a few seconds.
Add your chocolate chips and continue mixing just until flour is fully incorporated.
Preheat oven to 400°F and line two baking sheets with parchment paper. Scoop 12 small balls of dough onto each sheet with a melon baller (about 2 tbsp), spaced 1-2" apart.
Sprinkle a pinch of sea salt over each portion of dough and bake for 10-12 minutes until lightly golden brown.
Begin your frosting by combining 3/4 cup granulated sugar with 1/4 cup water and cream of tartar in a medium saucepan. Cook over medium high heat until bubbly and boiling.
Meanwhile, whip your egg white and 1/2 tsp vanilla in a stand mixer or by hand until medium-stiff peaks form. Then, carefully pour your hot sugar syrup into the egg white while whisking on high speed until it forms stiff peaks.
Once your cakes are cooled, transfer meringue frosting to a piping bag and snip a 2" hole at the end. Pipe a dollop onto 12 halves of cake and cover each with another cake.