Grease a 9 x 5 inch loaf tin
Once the dough has doubled in size, punch it down to release air and turn it onto a lightly floured surface. Roll it into a 12 inch by 10 inch rectangle. If the dough is shrinking and you're struggling to roll it out, let it rest for 5 - 10 minutes to help the gluten relax.
Spread the surface of the dough evenly with the frangipane and sprinkle with almond slices or crushed nuts. Roll the dough lengthwise, so you have a 12 inch tube. Cut the tube in half and twist the two halves together, making sure that the filling side is facing up. Place the dough braid in the greased loaf tin.
Cover and let rise for another 90 minutes. When you press your finger into the dough, the indent should fill halfway. If it fills all the way, let the dough proof for longer. If it doesn't fill at all and stays indented, bake immediately.
Towards the end of the proof, preheat the oven to 375°F. Beat together the egg and milk to create an egg wash. Once the loaf is finished proofing, brush the top with egg wash, avoiding the frangipane. Sprinkle with sliced almonds or crushed nuts.
Place the loaf in the middle of the oven and bake for 15 minutes. Check the loaf - if the top of the loaf is browning, tent with aluminum foil. Continue baking for another 15 - 20 minutes, for a total bake time of 30 - 35 minutes. The loaf should be golden brown and make a hollow noise when tapped. Remove from the oven and let cool for 20 minutes in the tin.