In a medium bowl, whisk together the flour, baking soda and salt. Set aside.
In a large bowl, beat the dairy free butter, peanut butter, granulated sugar and brown sugar for 2 minutes until fluffy. Beat in the egg, oat milk and vanilla until smooth.For the best texture, use a regular creamy peanut butter rather than a natural style one that separates.
Add the dry ingredients and mix on low speed until combined. Cover and chill the dough for 30 minutes.
Preheat the oven to 375°F and line two baking sheets with parchment paper. Roll the dough into 1 tablespoon balls, roll each one in the granulated sugar and place them 2 inches apart.
Bake for 8-10 minutes, until the cookies are puffed, lightly golden and just starting to crack.
Immediately press a chocolate chunk into the center of each hot cookie, letting the edges crack around it. Cool on the sheet for 5 minutes, then move to a wire rack and let the chocolate firm up before stacking.