Line a 9-inch round cake pan with cooking spray and parchment paper. Set aside.
Make the crumb topping: In the bowl of a stand mixer fitted with a paddle attachment, beat 1 ½ cups flour, brown sugar, cinnamon, ¼ teaspoon salt, and ¾ cup butter until mixture resembles wet sand.
Transfer to a small bowl and set aside.
Preheat oven to 350 F.
In the same stand mixer bowl, beat remaining ½ cup butter with granulated sugar until smooth.
Add eggs one at a time, mixing until each is combined with the creamed butter and sugar. , Scrape down the bowl with a rubber spatula after each addition if needed.
Add 1 ½ teaspoons vanilla extract, ½ cup sour cream, and lemon zest. Beat to combine.
Add 2 cups flour, baking powder, baking soda, and remaining ¾ teaspoon salt. Beat just until no flour remains visible.
Add remaining ½ cup sour cream. Beat until batter is smooth.
In a small bowl, toss blueberries with remaining 1 tablespoon flour to coat.
Pour cake batter into prepared pan and spread evenly.
Top with blueberries and 1 teaspoon lavender flowers.
Add crumb topping in an even layer.
Bake for 60 to 75 minutes or until a wooden pick inserted in the center comes out clean.
Transfer to a wire rack and cool for at least 1 hour.
Make the glaze: In a small bowl, stir to combine confectioners' sugar, remaining ½ teaspoon vanilla extract, ½ teaspoon lavender flowers, and 1 tablespoon lemon juice.
If the glaze is too stiff, stir in a splash of water or milk. Repeat if necessary until you get a pourable consistency. Add food coloring if desired.
Drizzle glaze over cake and sprinkle with remaining ½ teaspoon lavender and additional confectioners' sugar, if desired.