Whisk together flour, baking soda, baking powder, and salt. In another bowl, cream butter with sugar at high mixer speed. Add eggs, vanilla, and sour cream, beating at medium-high until combined.
Gently mix the wet and dry ingredients at low speed, then add milk until combined. You should have about 2 ½ cups of batter.
Spread half the batter into the pan, sprinkle half of the crumb mix over it, then layer on your remaining batter and sprinkle the rest of the crumb mixture on top.
Let your sweet cake bake away for 32 to 38 mins or 'til a toothpick inserted into the middle comes out mostly clean. Let the cake cool in its pan for about 15 minutes on a rack.