Start by making the filling. Line a small sheet pan with plastic wrap or parchment paper. Using a small spoon or teaspoon measure, scoop dollops of Biscoff spread out and place these dollops spaced out on the lined sheet. You'll need about 24 dollops of Biscoff (roughly half a cup of spread). Place these in the freezer to chill while you make your dough.
½ cup Biscoff spread
Preheat an oven to 350ºF and line a couple of baking trays with parchment paper.
In a large mixing bowl, cream together the butter, Biscoff, sugar and brown sugar until light and fluffy (about 2 minutes).
1¼ cup unsalted butter, ½ cup Biscoff spread, ¾ cup light brown sugar, ½ cup granulated sugar
Add the egg and vanilla to the batter and beat to combine.
1 large egg, 1 teaspoon vanilla extract
Sift the flour, baking soda, salt, cinnamon and nutmeg into the mixture and beat until just combined, ensuring there are no unmixed pockets of flour.
1½ cup all purpose flour, 1 teaspoon baking soda, 1 teaspoon salt, 1½ teaspoon ground cinnamon, ½ teaspoon ground nutmeg
Add the oats to the mixture and stir to combine then add the butterscotch chips and mix to distributed.
2½ cup rolled oats, 11 oz butterscotch chips
Scoop out a ball of dough, about 2 tablespoons worth, and gently flatten in the palm of your hand. Add one of your chilled Biscoff dollops to the center and envelope in the dough, rolling into a ball. Repeat this process to create your Biscoff filled oatmeal cookie dough balls.
Place the dough well spaced (at least 2 inches apart) on your lined baking tray. Then, bake in the center of the preheated oven for 12 minutes. Remove from the oven and let the cookies cool for about 5 minutes on the cookie sheet before removing to a wire rack to cool completely.