Grate 3 tablespoons of butter and mix with 1/2 cup flour and 1/4 cup sugar. Cut in with a fork until crumbly and set aside.

Caramel Sauce:

Place 3 tablespoons butter in the cake pan and put in the oven to melt. Once melted, mix in 1/2 cup brown sugar and 1 tablespoon water.

Spread rhubarb pieces over the caramel sauce in the pan.

Mix dry ingredients (1 1/2 cups flour, 2 teaspoons baking powder, pinch of salt, and 1/2 teaspoon lemon zest) in a bowl and set aside.

In another bowl, beat 6 tablespoons butter until fluffy. Add 1 1/2 cups sugar and beat well. Add eggs one at a time, beating after each.

Add half of the flour mixture and beat for one minute. Then add half the milk and beat. Repeat with remaining flour mixture and milk.

Pour the batter over the rhubarb and caramel in the pan. Sprinkle with the crumb topping.

Bake at 350°F for about 40 minutes, until a toothpick inserted in the center comes out clean.

Let the cake cool in the pan for 10 minutes. Loosen edges with a knife and invert onto a cooling rack. Let cool completely before enjoying!