Using a food processor, blend the coconut flakes into small pieces. Set aside for garnish. Rinse container for next step.
Drain pineapple juice from the can into a measuring cup. SAVE the pineapple juice. Pour half of the crushed pineapple into the food processor and blend until smooth. (Save the leftover pineapple for smoothies, etc.) Pour pureed pineapple into a small saucepan. (Rinse container for next step.) Add the brown sugar, cornstarch, 1 Tbsp of the pineapple juice (or water), and ½ tsp rum extract. Heat until boiling and thickened slightly. Remove from heat, and allow to cool completely in the refrigerator.
Blend blackberries in the food processor. Press mixture through a fine mesh sieve into a bowl. Set aside for frosting.
Meanwhile, preheat oven to 375 degrees Fahrenheit and line a muffin tin with 18 paper cups.
For the cupcakes: Using a stand mixer with the paddle attachment, cream the butter and sugars. Add the eggs, pineapple juice, coconut milk, and coconut extract. Mix well. Scrape the bowl.
In a separate bowl, mix the flour, baking soda, and salt. Add to wet mixture all at once and mix until just incorporated.
Use a #30 scoop and fill each muffin cup with a rounded scoop of batter (just over half full). Bake at 375 degrees Fahrenheit for 14 to 15 minutes, rotating the tray the last 4 to 5 minutes to cook the cupcakes evenly.
Once the cupcakes have baked, remove them from the tin and allow them to cool on a cooling rack in the refrigerator.
Meanwhile make the frosting. In the bowl of a stand mixer with the whisk attachment, whip the butter until smooth. Add half of the powdered sugar. Mix. In a small bowl mix together the blackberry puree, blackberry spread, and lemon juice. Add to the frosting. Mix and scrape the sides as needed. Add the remaining half of the powdered sugar until desired consistency. Mix well. Prepare a piping bag fitted with a Wilton 2D tip. Fill with frosting and set aside.
Once the cupcakes have cooled completely, use a paring knife to cut out a circle/cone shape from the center of each cupcake. Set the cupcake tops aside.
Place the pineapple filling in a sandwich size zip-top bag and cut off the corner. Pipe the filling equally amongst all 18 cupcakes. Place cupcake centers on top of the filling.
Pipe frosting on the top of each cupcake, from the outside in towards the center. Sprinkle with coconut flakes and place a blackberry in the center of the frosting. Enjoy!