Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy removal of cookies.
In a large mixing bowl, cream together the softened butter and granulated sugar using an electric mixer or whisk until the mixture is light and fluffy, about 2-3 minutes. Look for a pale, airy consistency with no visible lumps of butter.
Add the egg, vanilla extract, and the dissolved espresso powder to the creamed mixture. Mix on medium speed until well combined, and the mixture looks smooth and slightly increased in volume, with a fragrant aroma of coffee and spices.
In a separate bowl, whisk together the all-purpose flour, chai spice blend, and rolled oats. Gradually add this dry mixture to the wet ingredients, mixing on low speed or folding until just combined. The dough should be crumbly but hold together when pressed.
Use a cookie scoop or teaspoon to portion out the dough onto the prepared baking sheet, spacing cookies about 2 inches apart. Slightly flatten each cookie with the back of a spoon or your fingers for even baking.
Bake in the preheated oven for 10-12 minutes, until the edges are golden brown and the surface is set but still slightly chewy. The cookies will have a rustic, uneven appearance with a slightly cracked surface. Remove from the oven and allow to cool on the baking sheet for 5 minutes before transferring to a cooling rack.
