Stir together granulated sugar and cinnamon in a small bowl until combined. Set mixture aside. Generously butter a 1 qt. bundt pan or tube pan. Set pan aside.

Whisk flour, sugar, baking powder and salt together in a medium-sized bowl until combined ("dry ingredients"). In a SEPARATE bowl, whisk together milk, melted (cooled) butter, eggs and vanilla ("wet ingredients"). Pour "wet" ingredients into the "dry" ingredients, then whisk or stir until the batter is fully combined.

Using a large spoon, place HALF the batter in the buttered bundt pan, spreading it evenly. Sprinkle all the cinnamon/sugar mixture evenly over the batter. Using a butter knife or spatula, swirl it through the batter in a back-and-forth motion so cinnamon sugar is intertwined with the batter. Spoon remaining half of the batter on top; spread it out, being careful not to mix it with the cinnamon swirl layer.

Pour 1½ cups of water into the Instant Pot inner pan, then place a trivet on the bottom. Carefully lower the bundt pan down onto the trivet.

Lock the lid in place and flip the Pressure Release knob to SEALING. Set the MANUAL, CAKE or PRESSURE COOK setting to 35 minutes at high pressure. It usually takes the Instant Pot about 10 minutes to reach full pressure inside before it begins cooking at the time selected. Once cooking program has finished, let the internal pressure release NATURALLY for 10 minutes. After 10 minutes, flip the Pressure Release knob to VENTING, which releases all the remaining steam.

When all steam has been released, open the Instant Pot. Carefully lift hot pan out of the Instant Pot. Let cake cool (still in pan) on a wire rack for 5-7 minutes. Carefully run a butter knife around inside edges of pan. Invert pan onto the wire rack, then lift the pan off of the cake. If you buttered the pan well, the cake should slip out with no problem. Immediately turn cake right side up; let it cool for several minutes before adding icing.

Beat softened cream cheese, powdered sugar and vanilla in small bowl until lump-free and smooth. Spoon icing into a zip lock plastic bag; seal the bag. When cake has cooled a bit, cut a small bottom corner off the ziplock bag. IMPORTANT: If cake is too hot the icing will melt, so be patient! Place parchment paper, wax paper, or foil under wire rack. This helps catch any icing "drips", making cleanup easier. Squeeze bag to move icing to the cut corner, then apply in a decorative fashion to the surface of the cinnamon bundt cake.

Let icing firm up; slice cake into 8 wedges. Serve warm or at room temp. Enjoy!