Heat the oven to 350° F.
Line the muffin pan with the muffin cups.
In a large bowl, whisk the eggs, honey, lemon juice or vinegar, vanilla extract and espresso powder (if using; this will help it dissolve) until combined.
Add the almond flour, arrowroot, cocoa powder, baking soda and salt. Stir with a spatula until fully combined, with no visible almond flour left. (If your almond flour is very clumpy, sift it into the bowl with a fine-mesh sieve, pushing through any larger clumps.)
Stir in the ½ cup chocolate chips.
Scoop ¼ cup portions into each muffin cup. (If you have any extra better left, you might be tempted to add more to the muffins. Do not do this! It'll make the muffins rise too much and then collapse. Not the worst thing in the world but instead you can just make 1-2 extra muffins.)Sprinkle a few extra chocolate chips on top of each muffin. Bake for 17-20 minutes, rotating the pan halfway through, until the tops are puffed up and look dry.
Cool completely (on a cooling rack, if using), then drizzle with the melted chocolate.