Preheat the oven to 350°F (175°C). Grease a cake pan with butter or non-stick spray and set aside.
In a mixing bowl, combine the granulated sugar and melted butter until well blended and creamy, showing a smooth, pale mixture.
1 cup granulated sugar
Add the beaten eggs to the sugar-butter mixture gradually, whisking until the mixture is smooth and slightly thickened, with a glossy appearance.
1 cup granulated sugar
Sift together the flour, baking powder, and salt in a separate bowl. Gradually fold the dry ingredients into the wet mixture using a spatula until just combined, avoiding overmixing for a tender crumb.
1 cup granulated sugar
Gently fold the chopped rhubarb into the batter, distributing evenly without breaking the pieces, until all rhubarb is incorporated.
1 cup granulated sugar
Pour the batter into the prepared cake pan, spreading evenly with a spatula. Bake in the preheated oven for 40-45 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
Remove the cake from the oven and allow it to cool in the pan for 10 minutes before transferring to a wire rack to cool completely. The finished cake should have a moist crumb with vibrant rhubarb streaks visible throughout.