Crumble topping:

• 3/4 cup sugar
• 3 tablespoons flour
• 1 teaspoon salt
• 1/4 teaspoon ground nutmeg
• 1/2 teaspoon vanilla extract
• 1/2 stick (1/4 cup) cold butter, cut up

Coffeecake:

• 2 cups flour
• 1 teaspoon each: baking powder, baking soda
• 1/2 teaspoon each: nutmeg, salt
• 1 stick (1/2 cup) butter, at room temperature
• 1/2 cup sugar
• 2 eggs
• 1 teaspoon vanilla extract
• 1 cup sour cream
• 2 cups diced rhubarb

1. Heat the oven to 350 degrees.
2. For topping, combine the sugar, flour, salt and nutmeg in a bowl.
3. Stir in the vanilla; work in the butter with a pastry blender or fork until crumbly.
4. Set aside.
5. For cake, stir together the flour, baking powder, baking soda, nutmeg and salt in a bowl; set aside.
6. Beat together the butter and sugar in a mixing bowl until light and fluffy; beat in the eggs, one at a time.
7. Beat in vanilla.
8. Beat in half the flour mixture until creamy, then beat in sour cream until blended.
9. Beat in remaining flour mixture until combined.
10. Stir in rhubarb.
11. Spoon the batter into a buttered 9-inch tube pan; top with the crumble mixture.
12. Bake until a toothpick inserted in the center comes out clean, about 1 hour.
13. Cool the cake in the pan, about 5 minutes; remove to a wire rack to cool completely.