Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
In a mixing bowl, combine the blueberries with 1/4 cup of granulated sugar. Gently toss to coat and set aside.
In a large bowl, cream together the softened butter and remaining 3/4 cup of granulated sugar until light and fluffy. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In another bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the butter mixture, alternating with the milk, starting and ending with the flour mixture. Mix until just combined.
Fold in the blueberries gently to avoid breaking them. Pour the batter into the prepared cake pan and spread evenly.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
While the cake cools, whip the heavy cream with powdered sugar and lemon zest until soft peaks form.
Once the cake is completely cool, spread the whipped cream over the top. Serve immediately or refrigerate until ready to serve.