Preheat the oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a bowl, whisk together flour, cocoa powder, sugar, baking soda, baking powder, and salt.
Add egg, milk, vegetable oil, and vanilla extract to the dry ingredients and mix until smooth.
Slowly stir in hot coffee or hot water; the batter will be thin.
Fill cupcake liners three-quarters full and bake for 18 to 20 minutes.
Let cupcakes cool completely before filling.
To make the chocolate filling, heat cream until steaming but not boiling.
Pour hot cream over chopped chocolate and let sit for one minute, then stir until smooth and glossy.
Allow ganache to cool slightly to thicken.
Core out a small section from each cooled cupcake and spoon in the chocolate ganache.
Make the strawberry frosting by beating softened butter until creamy, about 2 to 3 minutes.
Gradually add powdered sugar, then mix in strawberry puree, vanilla extract, and salt.
Beat frosting until light and fluffy, adding more powdered sugar if needed for piping consistency.
Pipe a generous swirl of strawberry frosting on each cupcake.
Top cupcakes with fresh strawberry slices for garnish.
For presentation, slice a cupcake in half to reveal the chocolate filling and moist texture.