Preheat your oven to 350°F (175°C) and prepare a 9-inch round cake pan.

Cream together the softened butter and sugar until light and fluffy.

Incorporate the eggs one at a time, then mix in the whole milk.

Whisk together the flour, baking powder, and salt in a separate bowl and mix into the wet ingredients.

Fold in the chopped rhubarb gently until evenly distributed.

Pour the batter into the prepared cake pan and smooth the top.

Mix the sugar and cinnamon for the topping and sprinkle over the batter.

Bake for 40-45 minutes until golden and a toothpick comes out clean.

Cool in the pan for 15-20 minutes before transferring to a wire rack.