Heat oven to 350°F. Line a large baking sheet with parchment paper.
In a large bowl, beat the butter and brown sugar together until creamy. Add the eggs and vanilla and beat again, scraping sides of bowl as needed, until combined.
1 cup salted butter, 1 1/2 cups light brown sugar, 2 large eggs, 2 teaspoons pure vanilla extract
Add the flour, baking soda, baking powder, and salt, stirring just to combine. Mix in oatmeal, toffee bits, and milk chocolate chips.
1 3/4 cup all-purpose flour, 1 teaspoon baking soda, 1/2 teaspoon baking powder, 1/2 teaspoon salt, 3 cups old-fashioned oatmeal, 1 1/2 cups toffee bits, 1 cup milk chocolate chips
Drop dough by rounded spoonfuls onto the prepared baking sheet. I prefer making these cookies extra large with my cookie scoop, which is about 2 tablespoons of dough per cookie.
Bake for 12-14 minutes (if making large cookies) or 8-10 minutes (if you are making smaller ones, just until light golden brown around the edges. I prefer to underbake slightly for a chewier, softer cookie.
Cool cookies on the baking sheet for a few minutes before transferring to wire racks to cool completely.