• For the Topping
• Heat the oven to 350 degrees F.
• Spray the bottom and sides of an 8-inch square baking pan with non-stick cooking spray
• Combine the brown sugar, water, butter and salt in a small saucepan and bring to a boil, whisking occasionally.
• Then set aside to cool.

For the Cake

• Combine the flour, baking powder, cinnamon and salt in a medium mixing bowl.
• Combine the butter and sugar in a large mixing bowl and cream with an electric hand mixer on medium-high speed until fluffy, about 2 minutes.
• With the mixer on medium-low speed, add a third of the flour mixture to the bowl.
• Add half of the milk and the vanilla.
• Add another third of the flour, followed by the remaining milk and the rest of the flour.
• Scrape down the sides of the bowl and beat on medium speed for 30 seconds.
• Scrape the batter onto the prepared pan and smooth the top with a rubber spatula.
• Pour the topping over the batter (the pan will be very full).
• Carefully transfer the pan to the oven and bake until set for 45 to 50 minutes.
• Let the cake cool in the pan for 15 minutes.
• Invert it (turn it upside down) onto a large rimmed serving platter.
• Serve.