Preheat your oven to 350°F (175°C). Grease the springform pan with butter and dust with flour.

Wash and cut the rhubarb into 1-inch pieces. Toss with a tablespoon of sugar and let sit for 15 minutes.

Cream together the butter and sugar until light and fluffy. Add the eggs one at a time, mixing well after each.

In a separate bowl, whisk together the almond flour, all-purpose flour, baking powder, and a pinch of salt. Combine with the butter mixture, alternating with milk.

Pour the batter into the prepared pan. Arrange rhubarb on top, pressing lightly into the batter.

Bake for 45-50 minutes until golden brown and a toothpick comes out clean. Monitor in the final minutes to avoid overbaking.

Cool in the pan for 15 minutes, then remove the springform ring and cool completely on a wire rack.