Kohlrabi Carrot Bake

3 medium kohlrabi, peeled and sliced
4 medium carrots, sliced
1/4 cup chopped onion
3 TBLS butter, divided
2 TBLS all-purpose flour
1/2 tsp salt
dash black pepper
1 1/2 cups milk
1/4 cup minced fresh parsley
1 TBLS lemon juice
3/4 cup soft bread crumbs

-Steam carrots and kohlrabi until tender, about 15 minutes, and set aside
-In a large skillet, sauté onion in 2 TBLS butter until tender. Stir in the flour, salt and pepper until blended. Gradually whisk in the milk. Bring to a gentle boil and stir for 2 minutes, or until thickened.
-Remove from heat. Stir in the vegetable mixture, parsley and lemon juice. Transfer to a shallow 2-qt baking dish that has been lightly greased.
-In a small skillet, melt remaining butter over medium heat. Add bread crumbs. Cook and stir for 2-3 minutes or until lightly browned. Sprinkle over vegetable mixture.
-Bake, uncovered, at 350 degrees for 20-25 minutes or until heated through.