When layering the batter over the brown sugar and cinnamon, I found it works best to dollop the batter across the top and then gently spread it out, rather than trying to pour and spread all at once.
I also like to use a little less than half of the batter for the bottom layer so there’s a bit more to work with on top. The batter is thick, so it may pull slightly as you spread it, that’s completely normal. Just do your best to gently spread it out, then sprinkle the remaining brown sugar and cinnamon mixture over the top.
Once it bakes, everything comes together beautifully, so it doesn’t need to be perfect.
I have also made the batter in 1 bowl and it turns out just as good. Mix the wet ingredients in a large bowl first, then add dry ingredients (flour, sugar, baking powder and salt) and mix until combined.