Make the Dough:

1. Pour the warm milk into the bowl of a stand mixer and sprinkle with yeast. Let stand for 5 minutes to proof.
2. Stir in the cream and melted butter, then add the beaten egg, salt and 2 ½ cups of flour. Using the dough hook attachment, mix the dough at low speed until it starts to come together, adding the remaining ½ cup flour as it goes. (If the dough is still very wet and sticky, sprinkle in more flour, 1/4 cup at a time, until it's no longer sticky.)
3. Once the dough starts to pull together into a ball, increase speed to medium-low and knead for about 10 minutes or until the dough has pulled into a ball and feels soft and elastic.
4. Transfer the dough to a lightly oiled bowl, and cover with a clean dishcloth. Place in a warm, draft-free spot to rise until doubled in size, about 1.5 hours.

Prepare the Filling:

1. While the dough is rising, saute the bacon in a large heavy-bottomed skillet until it starts to crisp. Drain off all but 1 tbsp bacon fat. Add the green onions and saute for 2-3 minutes longer, or until the onions are soft but haven’t taken on any colour. Set aside to cool.

Assemble the Buns:

1. Once the dough has doubled in size, punch it down and knead 2-3 times. Divide into 16 equally-sized pieces, and roll each one out into a 5” circle.
2. Place a small dollop of mustard onto the middle of the circle using a scant ½ tsp measure, and top with a heaping tablespoonful of the bacon and green onion mixture. Bring the edges of the dough together to enclose the filling inside a ball, and pinch tightly to seal up the filling.
3. Arrange the buns about 2” apart on two large parchment-lined baking sheets (or arrange in two 9” round non-stick cake pans, if you prefer.) Cover with a clean dishtowel and let rise for 45 minutes.

Glaze and Bake the Buns:

1. Preheat the oven to 375F.
2. In a small bowl, stir together the mustard and honey until combined. Brush half of the glaze onto the buns, reserving the remainder for later.
3. In a second bowl, whisk together the flour and water to make a smooth paste. Scoop into a pastry bag fitted with a round tip, and pipe a paste cross onto the top of each bun.
4. Bake in preheated oven for 25 to 30 minutes, until golden brown. While the buns are still hot from the oven, brush with the remaining glaze. Let cool for 10 minutes, then transfer to a wire rack to finish cooling off completely (or serve right away, if you prefer to serve the buns still-wam.