Preheat the oven to 350 degrees
Chop 5 cups of rhubarb. Stir in the white sugar and lemon juice. Set aside.
In a mixing bowl, or in a stand mixer, cream the butter, brown sugar. Next, mix in the eggs and vanilla extract.
In a separate bowl, measure in the flour, baking powder and salt.
Measure out the milk. Add the milk and dry ingredients, alternating. Mix fully between each addition. Begin and end with the milk. *You can just dump it all in and mix it well. The alternating method is used to make the batter extra smooth. Prepare a 9 x 13 baking dish by lightly spraying or rubbing it down with a little oil.
Pour the rhubarb, along with all the juices from the sugar, into the prepared baking dish.
Pour the batter evenly over the rhubarb.
In a small saucepan, measure in the half & half and the corn syrup. Whisk, over heat, occasionally until it comes to a simmer. Drizzle the hot liquid slowly and carefully over the batter layer. Do NOT smooth or mix at all.
Place into the hot oven on a middle rack. Bake for 50 minutes.
Let sit and cool for at least 10 minutes before serving it up with ice cream.