Heat the milk over low heat until it reaches the temperature of warm bathwater. Take it off of the heat and sprinkle the yeast over the surface. Let stand until foamy. About 5 minutes.
Pour the milk and the yeast into the bowl of a stand mixer fitted with a dough hook. Add the honey, salt, half of the bread flour, and half of the whole wheat. Mix on medium-low until a dough forms.
Add the remaining whole wheat flour and mix until well integrated. Add a little or all of the remaining bread flour in 1/4 cup increments until the dough begins to clean the bowl. You may not need the whole cup.
When the dough feels tacky but not sticky, start adding the butter, a few cubes at a time. Wait until each addition is fully integrated before adding more.
Once the butter is fully integrated, transfer the dough to a lightly floured surface and knead until smooth and silky to the touch. This should take about 5-7 minutes.
Form the dough into a ball and transfer to a large bowl greased with olive oil. Cover and let rise until doubled in size. About an hour and a half.
Once the dough has risen, gently deflate and divide it into two. Take one half and flatten it into a rectangle. Roll it up to form a snake and pinch the seam to form a seal. Tuck either end inside the snake and pinch once again to form a seal. Refine the shape and transfer to a baguette pan or a baking sheet lined with parchment paper. Repeat with the remaining half.
Cover the two baguettes with a tea towel and preheat the oven to 375°F. Once the oven is up, whisk the egg and water together in a small bowl. Cut vents on the surface of each baguette and brush them with egg wash. Sprinkle the loaves with sesame seeds and place them in the oven. Bake for 30-35 minutes or until golden. Transfer to a cooling rack and let cool completely.