In a large sauté pan, add butter, sugar, and rum. Cook over medium heat, stirring frequently, until butter has melted and mixture starts to simmer. Add pineapple. Cook, stirring occasionally, until pineapple caramelizes, about 10 minutes. Set aside to cool.
Preheat oven to 425℉. Line a baking sheet with parchment paper.
In a large bowl whisk together flour, 2 tablespoons sugar, baking powder, and salt. Add butter and cut in with a pastry blender or your fingers until butter pieces are the size of small peas and mixture is crumbly.
In a measuring cup combine coconut milk and vanilla. Add to dry ingredients and stir until just combined.
Drop dough in 4 large spoonfuls onto prepared baking sheet, spacing them 2” apart.
In a small bowl, mix together remaining 2 teaspoons sugar and cinnamon. Sprinkle over biscuits and bake until golden brown, 15-20 minutes. Let cool 10 minutes before assembly.
Using a hand mixer, whip cream, sugar, rum (if using), and coconut extract until softly whipped.
To serve, split shortcakes in half, spoon whipped cream over the bottoms, followed by pineapple and nuts. Place other shortcake half on top and serve immediately.