Preheat your oven to 350°F (175°C). In a mixing bowl, cream together 1/2 cup softened unsalted butter and 1/4 cup granulated sugar until light and fluffy, about 3-4 minutes. Gradually add 1 cup of all-purpose flour and a pinch of salt, mixing until you achieve a sandy texture. Press the mixture firmly into the bottom of a parchment-lined 8x8-inch baking pan. Bake for 15-20 minutes, or until the crust is lightly golden.

While the crust is baking, whisk together 2 large eggs, 3/4 cup granulated sugar, 1/2 cup milk, and 1/4 cup cream in a sizable bowl. Ensure everything is well combined, then gently fold in 2 cups of chopped rhubarb. Set the custard mixture aside while the crust finishes baking.

Once the shortbread crust is golden brown, carefully pour the custard filling over the hot crust, spreading it evenly. Return the pan to the oven and bake for an additional 40-45 minutes, or until the custard is set and a slight jiggle remains in the center.

After baking, take the pan out of the oven and allow it to cool at room temperature for about 30 minutes. Once cooled, refrigerate for at least 2 hours until firm. To slice the Rhubarb Custard Bars, use a warm knife for clean edges.