Preheat oven to 350°F (175°C). Melt butter in a saucepan over medium heat, stir in brown sugar, cream, and salt, and cook until smooth, about 2 minutes. Pour into an ungreased Bundt pan and arrange pecans evenly.

Whisk flour, baking powder, baking soda, and salt for 30 seconds. Set aside.

Beat softened butter and granulated sugar with a mixer on medium until pale and fluffy, about 3 minutes.

Add eggs one at a time, then vanilla. On low, mix in half the flour, all the buttermilk, then remaining flour until just combined, about 1 minute. Stir once by hand.

Pour batter over the pecan base and smooth the top. Bake 45 to 50 minutes, until a toothpick comes out clean.

Cool in the pan for 10 minutes. Run a knife around the edges, invert onto a plate, and lift off the pan. Let cool completely.