Preheat the oven to 350°F. Line a 8"x8" square pan or 8" springform pan with parchment paper and grease all sides with butter or oil. Set aside.
In a small bowl, add corn starch and blueberries. Toss to coat together and set aside.
In a small bowl, combine sugar and lemon zest. Rub between finger tips to massage the lemon oils into the sugar. Set aside.
In a medium bowl, whisk together the sugar, melted butter and eggs until fluffy and light yellow. Add sour cream and vanilla extract. Whisk to combine.
Add sour cream and heavy cream. Whisk to combine.
Whisk in the dry ingredients until no more flour is visible. Gently fold the blueberries into the cake batter. Note: If substituting fresh with frozen, do not overmix because the batter will turn blue color.
Spread batter into prepared baking pan. Sprinkle with blueberries, sliced almonds and lemon sugar. Bake for 40-43 minutes until golden brown on top and a toothpick in inserted to the center and it comes out clean. Do not overbake.
