Preheat oven to 350F. Butter 9" cake pan.
Topping: Combine flour, sugar and salt and rub in the butter by hand until the mixture becomes crumbly. Refrigerate until needed.
Cake: Cream together butter and sugar before adding eggs one at a time. Incorporate vanilla, lemon juice and zest, and yogurt. Mix on low speed until ingredients are just combined and a bit lumpy.
Evenly smooth batter into pan and evenly cover with struesel. Bake until no longer jiggly, 55-65 minutes. Cake will be moist and may not pass toothpick test.
Let atand for 15 minutes before serving.