Hummingbird IPA Cake with Caramel Buttercream

Name: Hummingbird IPA Cake with Caramel Buttercream
Ingredients: 1 cup granulated sugar; 1 cup heavy cream, at room temperature; 2 sticks (1 cup) unsalted butter, softened; 2 cups confectioners' sugar; 1 tablespoon poppy seeds, lightly toasted and cooled; 1 teaspoon vanilla extract; 1/2 teaspoon kosher salt; Unsalted butter, for greasing the pans; 2 1/2 cups all-purpose flour, plus more for pan (see Cook's Note); 1 1/4 teaspoons ground cinnamon; 3/4 teaspoon baking soda; 3/4 teaspoon kosher salt; 1 cup sweetened shredded coconut; 2/3 cup finely chopped walnuts; 1 cup mashed ripe banana (from about 3 medium bananas); 2/3 cup canola oil; 2/3 cup granulated sugar; 2/3 cup packed dark brown sugar; 1 1/4 teaspoons vanilla extract; 2 large eggs; One 12-ounce bottle IPA