Preheat oven to 325 degrees F. Spritz an 8" x 8" baking pan with cooking spray.

To make the crumb topping, in a small bowl, combine the brown sugar, 2 tablespoons flour blend, cinnamon and nutmeg. Cut in the butter until crumbly. Toss in the pecans. Set aside.

In a medium bowl, sift together the 1 1/4 cups flour blend, baking powder and salt.

Beat the butter and granulated sugar until creamy in a large bowl. Beat in the egg. Add the flour mixture and beat until incorporated. Slowly add the kefir or milk while beating on low until blended. Fold in the rhubarb.

Pour batter into prepared baking pan. Sprinkle evenly with the crumb topping. Bake 45 to 50 minutes, or until golden on top and cake tests done with a toothpick. Cool completely.

To make the glaze, combine the confectioners' sugar, 2 teaspoons milk and vanilla in a small bowl. Stir until smooth. Add more milk by the teaspoon if needed to achieve drizzling consistency. Drizzle over top of the cooled cake. Cut into pieces and serve.