Preheat oven to 350.

Make the topping first.  In a medium sized bowl, mix brown and white sugars, cinnamon and salt.  Whisk together to combine well.  Add the warm, melted butter.  Add the flour and toss the mixture with a fork or your hands until moist clumps form.  Set aside.

Then move on to the cake. Butter a 13x9x2-inch glass baking dish.  Sift together the flour, baking soda, baking powder and salt into a medium bowl.  In a large bowl, beat the room temperature butter with an electric mixer until smooth.  Add the sugar and blend until light and fluffy.  Add eggs one at at time, beating mixture after adding each one.  Add the Skyr and vanilla extract and beat until just blended.

Add flour mixture in 3 parts, beating after each addition until just incorporated. Transfer batter to baking pan and smooth evenly with a rubber spatula.  Squeeze small of the topping mixture together to form small clumps and sprinkle evenly over the top of the batter, completely covering the batter.

Bake the cake at 350 for about 45-50 minutes, until a knife comes out clean and the topping is deep golden brown and slightly crisp.   Cool for about 30 minutes  Serve.