Preheat the oven to 350F. Grease & line a standard (9x5") loaf pan w/ parchment paper; set aside.
Brown the butter for the cake. Add the ½ cup butter to a saucepan over medium-high heat. Allow to melt & slightly brown (~5 mins). Remove & immediately pour into a large bowl. Set aside to cool slightly.
Crumb topping: In a medium bowl, combine the flour, cinnamon, both sugars & butter. Mix until it resembles wet sand. Then, mix in the chocolate chips. Place in the fridge to chill.
Continue cake batter. In a medium bowl, whisk together the flour, baking powder & salt. Set aside.
Once the brown butter has slightly cooled, add the sugar and whisk. Add in the eggs & whisk until fully incorporated.
Then, add in the greek yogurt, milk & vanilla. Whisk to combine.
Add dry ingredients to the wet. Mix until just combined & there are no large clumps of flour; do not to over-mix.
Gently fold in the chocolate chips.
Pour the batter into the prepared pan & evenly spread. Then, sprinkle the crumb topping all over.
Bake at 350F for 60-70 mins, until golden & a toothpick inserted comes out clean. Check the loaf at ~50 mins; if it is getting too brown, tent w/ foil.
Remove from the oven & let cool in the pan for at least 10-15 mins. Then remove & transfer to a serving plate or wire cooling rack. Slice & serve warm with butter & flaky sea salt, if desired.
