Heat oven to 350°F. Lightly grease mini muffin tins. Mix together flour, cornmeal, baking powder and salt; set aside. In a bowl, whisk egg, milk and butter together, then add zest, dill and capers. Add liquid to dry ingredients and mix until just combined (don't overmix).
Fill each mini muffin cup with a generous tablespoon of batter. Bake 18 to 20 min, until muffins spring back when touched. Cool in tins 5 min. Run a knife around edge of each muffin to remove from tins, then cool completely.
Cut the very top off of each muffin to create a flat surface. Top with a bit of salmon and a dollop of crème fraîche. Garnish with a dill sprig.
Save time on party day by making the muffins up to a day in advance; store airtight until ready to serve.