Preheat your oven to 350°F (175°C) and prepare a 9x13-inch baking pan by lining it with parchment paper or greasing it with butter.

In a mixing bowl, combine all-purpose flour and sugar. Cut in the butter until the mixture resembles coarse crumbs. Press into the base of the prepared pan and bake for about 10 minutes.

Whisk together sugar, flour, half-and-half, eggs, and vanilla extract until smooth. Fold in the diced rhubarb.

Pour the rhubarb custard filling over the hot crust and bake for 40-50 minutes, until the custard is set.

Allow the bars to cool at room temperature, then refrigerate for at least 2 hours.

For the topping, beat together cream cheese, powdered sugar, and vanilla. Fold in whipped topping, then spread over the cooled bars.

Refrigerate until ready to serve, then cut into squares.