Place the sugar in a medium saucepan over medium heat. Let the sugar melt and turn an amber color, about 3-4 minutes. Do not stir, but swirl the pan around to make sure the sugar is caramelizing evenly. Watch it so it doesn't burn.

Once the sugar is all melted, remove from heat and add the heavy cream in a small stream. It's okay if it gets a little lumpy. Return the pan to medium heat and cook while stirring until smooth.

Pour into a 2 cup or larger liquid measuring cup. Add the lemon juice and just enough milk to measure 1 cup. Set aside.

Preheat oven to 350 degrees F. Butter and flour a bundt cake pan.

In the bowl of a stand mixer fitted with a paddle attachment, mix the butter and brown sugar together until light and creamy. Add the eggs one at a time, mixing after each. Add the vanilla.

In a bowl, combine the flour, baking powder, baking soda, and salt. Add to the mixing bowl in three additions, alternating with the caramel liquid and ending with the flour mixture. Scrap down the bowl as necessary.

Pour into the prepared bundt pan and bake until a toothpick inserted comes out clean, 45-55 minutes. Let cool in the pan 10 minutes, then invert onto a wire rack to cool completely.

Beat the butter, powdered sugar, salt, and vanilla and the caramel liquid until smooth. Add additional tablespoons of the caramel liquid to reach desired consistency.

Frost the bundt cake. Store in an air tight container at room temperature, it will keep for several days.

Place the sugar in a medium saucepan over medium heat. Let the sugar melt and turn an amber color, about 3-4 minutes. Do not stir, but swirl the pan around to make sure the sugar is caramelizing evenly. Watch it so it doesn't burn.

Immediately pour the caramel onto a sheet pan lined with parchment or a silicone baking mat. Let cool 5 minutes, then break into pieces and decorate cake as desired.