Blueberry Muffin Baked Oatmeal

Name: Blueberry Muffin Baked Oatmeal
Ingredients: Unsalted butter (for pan); 2½ cups old-fashioned oats; ¾ cup sliced almonds, divided; 3 Tbsp. chia seeds; 1 tsp. baking powder; 1½ cups fresh or frozen blueberries; 1 large egg; ½ cup almond butter; ½ cup (packed; 100 g) dark brown sugar; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt; ½ tsp. ground cinnamon; ¼ tsp. freshly ground nutmeg; ½ tsp. almond extract (optional); ½ tsp. vanilla extract; 2½ cups milk of choice, divided; plus more for serving (optional); ¼ cup blueberry jam; Pure maple syrup (for serving; optional); Zest of 1 lemon (optional)