Preheat oven to 350°F/180°C, grease a 9-inch square baking pan and set aside.
In a medium bowl, stir together the flour, brown sugar and cinnamon for the topping.
To make the filling/topping, In a medium bowl, stir together the flour, brown sugar and cinnamon.
Then add the butter and mash it in with a spoon until the consistency is like sand with some clumps. Set the filling mixture aside.
Make the cake by mixing together the flour, baking powder, baking soda and salt in a mixing bowl; set aside
In a large bowl, cream butter and sugar until smooth, then add the eggs one at a time and mix well after each. Add the vanilla and stir well.
Add half of the flour and mix it in.
Then add half of the sour cream and stir until combined.
Repeat until all of the flour and all of the sour cream are mixed into the cake batter.
Carefully spread half of the batter on the bottom of the prepared baking pan.
Then add half of the crumble mixture to cover the layer of batter.
Spoon the remaining batter in small scoops over the surface of the filling, then very gently spread the scoops to create a uniform layer.
Top the coffee cake with the remaining crumb mixture, then bake in a preheated oven for 35 minutes, or until it's golden brown and a toothpick inserted into the center comes out clean. Allow the cake to cool completely.
Prepare the glaze by mixing together the powdered sugar and half and half until desired consistency is reached.
When the cake is completely cooled, drizzle the glaze over it.