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 1 cup sugar and 1/2 cup 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.
06 -
Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
07 -
For the butter sauce, combine 1/2 cup butter, 1 cup sugar, and the heavy cream in a saucepan over medium heat. Cook, stirring, until the sugar is dissolved and the sauce is smooth. Remove from heat and stir in 1 teaspoon vanilla extract.
08 -
Serve the warm cake drizzled with the butter sauce.