Melt 4 tablespoons of butter in a small pot over medium heat. Once melted, add ½ cup light brown sugar. Stir to combine. Cook over medium heat for 3 minutes, stirring occasionally, until the sugar dissolves and the mixture darkens slightly in color. Remove from the heat and add the heavy cream. Whisk until smooth. Add the almonds and stir to combine.

Pour the mixture into the prepared cake pan and smooth it into an even layer. Transfer to the refrigerator for 15 minutes.

Place the blueberries in a bowl. Cover with 1 tablespoon of granulated sugar and 1 tablespoon of cornstarch. Add 1 teaspoon lemon zest. Stir to coat.

Sift ¾ cup cake flour, 1 teaspoon baking powder, and ¼ teaspoon kosher salt into a small bowl. Set aside.

Using an electric hand mixer, cream 4 tablespoons butter with ½ cup light brown sugar in a large mixing bowl until light and fluffy. Add 1 egg and beat until smooth. Add 2 tablespoons lemon juice, 1 teaspoon lemon zest, and 1 teaspoon vanilla extract. Beat until just incorporated.

Add half the dry ingredients and beat with the mixer until just combined. Add half of the milk and beat until incorporated. Add the remaining dry ingredients and the rest of the milk. Beat until just combined. Don’t over-mix!

Remove the cake pan from the refrigerator.

Arrange the blueberries in the cake pan in an even layer. Press them gently into the caramel to create a tight layer. Avoid breaking them too much.

Spoon the batter over the blueberries and smooth it into an even layer.

Transfer the cake to the oven and bake for 50 minutes, or until a toothpick inserted into the center of the cake comes out clean.

Let the cake stand for 30 minutes at room temperature. The cake should still be warm to the touch when you invert it.

Place a large plate over the cake pan and carefully flip the cake onto the plate. Use a small butter knife to tap over the pan to encourage the release of the cake. Once the cake has been inverted onto the plate, peel away and discard the parchment paper. Cut the cake and serve it with vanilla ice cream on top. Enjoy!