01 -
Preheat the oven to 350°F (175°C) and grease a 9-inch square baking pan.
02 -
In a medium bowl, whisk together the flour, baking powder, and salt.
03 -
In a large bowl, cream together the sugar and softened butter until light and fluffy. Beat in the egg and vanilla extract.
04 -
Gradually add the flour mixture to the creamed mixture alternately with the milk, starting and ending with the flour mixture. Fold in the chopped rhubarb.
05 -
Pour the batter into the prepared pan and spread evenly. Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
06 -
In a saucepan over medium heat, combine the butter, sugar, and heavy cream. Cook, stirring constantly, until the sugar is dissolved, and the sauce is smooth. Remove from heat and stir in the vanilla extract.
07 -
Serve the warm cake drizzled with the butter sauce.