Preheat the oven to 350*.
whisk the flour, salt, baking powder, and baking sida togeather and set aside
Whip butter for about 2 minutes until light and creamy
Add the zest of both lemons and the sugar. Cream togeather for 4 to 5 minutes
Add in eggs one at a time, combining well after each.
Add the vanilla, yogurt, and buttermilk, and mix to combine.
Mix in the flour mixture and combine.
Spoon batter into prepared pan, filling them about ½ full with muffin batter.
Drop about a tablespoon of lemon curd into the center of each muffin, and cover with a thin layer of muffin batter. The cups should be about ¾ full. Then generously top with streusel crumb. Gently press the crumb to stick to the batter.
Bake for about 25 minutes or until the muffin has set and the crumbs get nice golden brown color.