Heat the oven to 375°F (190°C). Grease a 9 x 13-inch (23 x 33 cm) baking dish evenly with the softened 1 tablespoon (14 g) butter.

Heat a 12-inch (30 cm) skillet over medium heat. Add the breakfast sausage, along with the optional 1 teaspoon (5 ml) oil only if the sausage is very lean. Cook for 7 to 9 minutes, breaking it into small bite-size crumbles, until browned and fully cooked. Pork sausage should reach 160°F (71°C).

Transfer the cooked sausage to a paper-towel-lined plate or drain away excess grease. Let it cool slightly while you prepare the batter. Removing excess fat helps prevent a greasy or heavy casserole.

In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until evenly combined.

In a medium bowl, whisk the eggs until blended. Add the buttermilk, 1/4 cup (60 ml) maple syrup, melted butter, and vanilla. Whisk until smooth.

Pour the wet mixture into the dry ingredients: Fold gently with a rubber spatula just until no large pockets of dry flour remain. A few small lumps are fine. The batter should be thick but pourable; overmixing can make the casserole dense.

Spread about half of the pancake batter evenly in the prepared baking dish. Scatter the cooked sausage over the surface, then spoon and gently spread the remaining batter on top. Some sausage may remain visible, which is fine.

Bake at 375°F (190°C) for 30 to 35 minutes, or until the top is lightly golden and the center springs back when gently pressed. A toothpick inserted into a pancake-heavy section near the center should come out without wet batter.

If the edges are browned but the center still looks wet or jiggles like uncooked batter, continue baking for 3 to 5 minutes and check again. Avoid covering the dish unless the top is becoming too dark.

Remove the casserole from the oven and let it rest for 5 minutes before slicing into 12 pieces. Serve warm with optional maple syrup.