Preheat the oven to 325 degrees F (165 degrees C).
Cream together Butter (1/2 cup), Granulated Sugar (3/4 cup), Vanilla Extract (2 teaspoon), and Egg (2) with an electric mixer.
In a separate bowl, sift All-Purpose Flour (2 cup), Salt (1/2 teaspoon), Baking Powder (1/2 teaspoon), and Baking Soda (1/4 teaspoon).
Put half of the flour mixture into the butter and stir. Pour the Buttermilk (3/4 cup) into the batter, and mix together for about 30 seconds, and then add the rest of the flour mixture. Mix until well incorporated.
Fold in the Fresh Blueberries (1 cup) and Blueberry Jam (1/2 cup) until just marbled. Pour into a well-oiled 9-inch cake round.
Add Butter (1/4 cup) to a bowl, then add All-Purpose Flour (3/4 cup), Brown Sugar (1/2 cup), and Ground Cinnamon (1/4 teaspoon). Mix with your hands until mixture forms a crumble.
Sprinkle crumble on top of the cake along with the Fresh Blueberries (1/3 cup) and dot with the Blueberry Jam (2 tablespoon). Bake in the oven for 45-50 minutes or until a toothpick inserted in the center comes out clean.
Serve warm or at room temperature.